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Background: Despite the global public health threat posed by carbapenem-resistant Enterobacter spp., clinical and molecular epidemiological studies on international isolates remain scarce. Historically, the taxonomy of Enterobacter has been challenging, limiting our understanding of the clinical characteristics and outcomes of carbapenemase-producing Enterobacter spp. infections., Methods: Hospitalized patients enrolled in the CRACKLE-2 study (ClinicalTrials.gov, NCT03646227) from 2016-2018 with cultures positive for carbapenemase-producing Enterobacter spp. were included. Clinical and microbiologic data were collected from health records. Whole genome sequencing was performed, and the population structures of selected predominant clones were analyzed., Results: We enrolled 136 hospitalized patients with carbapenemase-producing Enterobacter spp. from 30 hospitals in 7 countries. Among the 136 isolates, eleven Enterobacter species were identified, with most isolates belonging to E. xiangfangensis (n=81, 60%) and E. hoffmannii (n=17, 13%), and carrying blaKPC (n=106, 78%) and blaNDM (n=12, 9%). Clinical characteristics and outcomes were similar among patients with E. xiangfangensis, E. hoffmannii or the other Enterobacter spp. 30-day mortality was 20% and older age at enrollment (adjusted odds ratio 1.42, 95% confidence interval 1.08-1.87) was associated with increased mortality. Sequence type (ST)171 E. xiangfangensis, ST78 E. hoffmannii, and ST93 E. xiangfangensis were the predominant clones, and the acquisition of fluoroquinolone resistance-associated mutations and carbapenemase-encoding plasmids contributed to their formation and global dissemination., Conclusions: Our findings demonstrated that E. xiangfangensis and E. hoffmannii are common species among international carbapenemase-producing Enterobacter spp., potentially linked to the clonal spread of a few predominant clones that have acquired fluoroquinolone resistance and carbapenemase-encoding plasmids., (© The Author(s) 2024. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Background: The CDC reported a 35% increase in hospital-onset (HO) carbapenem-resistant Enterobacterales (CRE) infections during the COVID-19 pandemic. We evaluated patient outcomes following HO and community-onset (CO) CRE bloodstream infections (BSI)., Methods: Patients prospectively enrolled in CRACKLE-2 from 56 hospitals in 10 countries between 30 April 2016 and 30 November 2019 with a CRE BSI were eligible. Infections were defined as CO or HO by CDC guidelines, and clinical characteristics and outcomes were compared. The primary outcome was desirability of outcome ranking (DOOR) 30 days after index culture. Difference in 30-day mortality was calculated with 95% CI., Results: Among 891 patients with CRE BSI, 65% were HO (582/891). Compared to those with CO CRE, patients with HO CRE were younger [median 60 (Q1 42, Q3 70) years versus 65 (52, 74); P < 0.001], had fewer comorbidities [median Charlson comorbidity index 2 (1, 4) versus 3 (1, 5); P = 0.002] and were more acutely ill (Pitt bacteraemia score ≥4: 47% versus 32%; P < 0.001). The probability of a better DOOR outcome in a randomly selected patient with CO BSI compared to a patient with HO BSI was 60.6% (95% CI: 56.8%-64.3%). Mortality at 30-days was 12% higher in HO BSI (192/582; 33%) than CO BSI [66/309 (21%); P < 0.001]., Conclusion: We found a disproportionately greater impact on patient outcomes with HO compared to CO CRE BSIs; thus, the recently reported increases in HO CRE infections by CDC requires rigorous surveillance and infection prevention methods to prevent added mortality., (© The Author(s) 2024. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Objectives: To evaluate causes of fever, including resistance patterns, in patients undergoing cancer treatment in Malawi., Methods: In this prospective cohort study, enrolled patients undergoing chemotherapy at Kamuzu Central Hospital in Lilongwe, Malawi were given a thermometer. If a temperature of ≥38°C was recorded, they were instructed to return for hospitalization, standardized fever workup, and antibiotics. All patients were followed through 90 days post-fever event or completion of chemotherapy., Results: One hundred and five patients were screened and 50 were enrolled. Of the enrollees, 26 (52%) were men and 26 (52%) were HIV positive, with a mean ART duration of 7 years and CD4 count of 293 cells/µL. The most common diagnoses were aggressive non-Hodgkin lymphoma (40%) and Hodgkin lymphoma (22%). Twenty-three febrile events were recorded from 15 patients. Of the 23 events, a causative agent was isolated in 13 cases: Escherichia coli (6), Plasmodium falciparum (3), Streptococcus pneumoniae (2), Pseudomonas aeruginosa (1) and Citrobacter freundii (1). Of the six E. coli isolates, all were found to be resistant to fluoroquinolones and 4/6 (66%) were resistant to cephalosporins. All patients but one survived; the death was attributed to Pseudomonas bacteraemia., Conclusions: This study describes laboratory-confirmed causes of neutropenic fever (NF) in cancer patients in Malawi. Gram-negative rods, followed by malaria, were the most common source of infection. Gram-negative rods were associated with high rates of antimicrobial resistance. Malaria and resistant bacterial infections should be considered for NF treatment and prevention in sub-Saharan Africa., (© The Author(s) 2024. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy.)

Competing Interests: Potential conflicts of interest. D. v. D. has National Institutes of Health funding unrelated to this work and has received grants from Merck and consulting fees and honoraria from Shionogi, Merck, Union, Roche, Qpex, Pfizer, Entasis, and Clinical Care Options. J. M. C. R. reports no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

Background: Use of anti-carbapenem-resistant Enterobacterales (anti-CRE) agents such as ceftazidime/avibactam has been associated with improved clinical outcome in cohorts that primarily include patients infected with CRE that are resistant to meropenem (MCRE)., Objectives: To clarify whether patients with CRE resistant to ertapenem but susceptible to meropenem (ertapenem-only-resistant Enterobacterales; EORE) benefit from therapy with anti-CRE agents., Methods: Patients treated for CRE infection in hospitals in the USA between 2016 and 2019 and enrolled in the CRACKLE-2 study were included. The primary outcome was the desirability of outcome ranking (DOOR) assessed at 30 days after index cultures., Results: The EORE group included 213 patients and the MCRE group included 643. The demographics were similar between the groups except for the patients' race and origin before admission. The MCRE group received anti-CRE agents for definitive therapy significantly more frequently compared with the EORE group (30% versus 5% for ceftazidime/avibactam). We did not observe a significant difference between the groups in the adjusted DOOR probability of a more desirable outcome for a randomly selected patient in the EORE group compared with the MCRE group (52.5%; 95% CI, 48.3%-56.7%). The MCRE group had a similar proportion of patients who died at 30 days (26% versus 21%) and who were discharged to home (29% versus 40%), compared with the EORE group., Conclusions: Patients with clinical EORE infection rarely received anti-CRE agents, but attained similar outcomes compared with patients with MCRE infection. The findings support current IDSA treatment guidance for meropenem- or imipenem-based therapy for treatment of EORE infections., (© The Author(s) 2024. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Background: Stenotrophomonas maltophilia is a carbapenem-resistant Gram-negative pathogen increasingly responsible for difficult-to-treat nosocomial infections., Objectives: To describe the contemporary clinical characteristics and genome epidemiology of patients colonized or infected by S. maltophilia in a multicentre, prospective cohort., Methods: All patients with a clinical culture growing S. maltophilia were enrolled at six tertiary hospitals across Japan between April 2019 and March 2022. The clinical characteristics, outcomes, antimicrobial susceptibility and genomic epidemiology of cases with S. maltophilia were investigated., Results: In total, 78 patients were included representing 34 infection and 44 colonization cases. The median age was 72.5 years (IQR, 61-78), and males accounted for 53 cases (68%). The most common comorbidity was localized solid malignancy (39%). Nearly half of the patients (44%) were immunosuppressed, with antineoplastic chemotherapy accounting for 31%. The respiratory tract was the most common site of colonization (86%), whereas bacteraemia accounted for most infection cases (56%). The 30 day all-cause mortality rate was 21%, which was significantly higher in infection cases than colonization cases (35% versus 9%; adjusted HR, 3.81; 95% CI, 1.22-11.96). Susceptibility rates to ceftazidime, levofloxacin, minocycline and sulfamethoxazole/trimethoprim were 14%, 65%, 87% and 100%, respectively. The percentage of infection ranged from 13% in the unclassified group to 86% in genomic group 6A. The percentage of non-susceptibility to ceftazidime ranged from 33% in genomic group C to 100% in genomic groups 6 and 7 and genomic group geniculate., Conclusions: In this contemporary multicentre cohort, S. maltophilia primarily colonized the respiratory tract, whereas patients with bacteraemia had the highest the mortality from this pathogen. Sulfamethoxazole/trimethoprim remained consistently active, but susceptibility to levofloxacin was relatively low. The proportions of cases representing infection and susceptibility to ceftazidime differed significantly based on genomic groups., (© The Author(s) 2024. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Background: Equitable representation of members from historically marginalized groups is important in clinical trials, which inform standards of care. The goal of this study was to characterize the demographics and proportional subgroup reporting and representation of participants enrolled in randomized controlled trials (RCTs) of antibacterials used to treat Staphylococcus aureus infections., Methods: We examined randomized controlled registrational and strategy trials published from 2000 to 2021 to determine the sex, race, and ethnicity of participants. Participant to incidence ratios (PIRs) were calculated by dividing the percentage of study participants in each demographic group by the percentage of the disease population in each group. Underrepresentation was defined as a PIR < 0.8., Results: Of the 87 included studies, 82 (94.2%) reported participant sex, 69 (79.3%) reported participant race, and 20 (23.0%) included ethnicity data. Only 17 (19.5%) studies enrolled American Indian/Alaskan Native participants. Median PIRs indicated that Asian and Black participants were underrepresented in RCTs compared with the incidence of methicillin-resistant S. aureus infections in these subgroups. Underrepresentation of Black participants was associated with a larger study size, international sites, industry sponsorship, and phase 2/3 trials compared with phase 4 trials (P < .05 for each). Black participants had more than 4 times the odds of being underrepresented in phase 2/3 trials compared with phase 4 trials (odds ratio, 4.57; 95% confidence interval: 1.14-18.3)., Conclusions: Standardized reporting methods for race and ethnicity and efforts to increase recruitment of marginalized groups would help ensure equity, rigor, and generalizability in RCTs of antibacterial agents and reduce health inequities., Competing Interests: Potential conflicts of interest. All authors report funding support from the ARLG of the National Institutes of Health (NIH) and the National Institute of Allergy and Infectious Diseases (NIAID; UM1AI104681). J. G. P. reports grants or contracts paid directly to her institution from NIH/NIAID (K01AI143881) and grants or contracts paid directly to her department from the Texas A&M Triads for Transformation and Montague-CTE. D. v. D. reports grants or contracts paid directly to his institution from NIH and Merck and grants or contracts paid directly to him from Shionogi Inc; consulting fees paid directly to him from Actavis, Tetraphase, Sanofi-Pasteur, Medimmune, Astellas, Merck, Allergan, T2Biosystems, Roche, Achaogen, Neumedicine, Shionogi, Pfizer, Entasis, Qpex, Wellspring, Karius, and Utility; honoraria paid directly to him from Pfizer; and an editor's stipend paid directly to him from British Society for Antimicrobial Chemotherapy. H. F. C. reports royalties from the Sanford Guide to Antimicrobial Therapy; payment for expert testimony from Nexus Pharmaceuticals; participation on a Merck Data Safety and Monitoring Board for molnupiravir, and stock ownership in Moderna and Merck. V. G. F. reports personal fees from Novartis, Debiopharm, Genentech, Achaogen, Affinium, Medicines Co., MedImmune, Bayer, Basilea, Affinergy, Janssen, Contrafect, Regeneron, Destiny, Amphliphi Biosciences, Integrated Biotherapeutics; C3J, Armata, Valanbio; Akagera, Aridis, Roche Astra Zeneca, and Pfizer; grants from NIH, MedImmune, Allergan, Pfizer, Advanced Liquid Logics, Theravance, Novartis, Merck; Medical Biosurfaces; Locus; Affinergy; Contrafect; Karius; Genentech, Regeneron, Deep Blue, Basilea, Janssen; Royalties from UpToDate, stock options from Valanbio and ArcBio, honoraria from Infectious Diseases of America for his service as Associate Editor of Clinical Infectious Diseases (2017–2022), and a patent sepsis diagnostics pending; support from Contrafect to present phase 2 data at 2019 ECCMID. M. M. P. reports grants or contracts paid directly to her institution from NIH/NIAID (R01AI019641), Centers for Disease Control and Prevention (NU50CK000488), and Green Acres Foundation; honoraria paid to directly to her from the US State Department for participation on a panel about antimicrobial resistance; payment from the American Society for Microbiology for travel to present research findings on antimicrobial resistance not directly related to this project; and unpaid participation on the Connecticut Department of Public Health Multidisciplinary Antimicrobial Resistance/Antimicrobial Stewardship Advisory Group. H. F. C. reports participation on a Data Safety Monitoring Board or Advisory Board for Merck (molnupiravir); stock from Moderna and Merck. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2024. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: In the USA, nirmatrelvir/ritonavir is authorized for the treatment of mild-to-moderate COVID-19 in patients at least 12 years of age, at high risk for progression to severe COVID-19., Objectives: To estimate the impact of outpatient nirmatrelvir/ritonavir on COVID-19 hospitalization risk in a US healthcare system., Methods: We conducted a cohort study using electronic health records among outpatients with a positive SARS-CoV-2 PCR test between January and August 2022. We evaluated the association of nirmatrelvir/ritonavir therapy with time to hospitalization by estimating adjusted HRs and assessed the impact of nirmatrelvir/ritonavir on predicted COVID-19 hospitalizations using machine-learning methods., Results: Among 44 671 patients, 4948 (11%) received nirmatrelvir/ritonavir, and 201 (0.4%) were hospitalized within 28 days of COVID-19 diagnosis. Nirmatrelvir/ritonavir recipients were more likely to be older, white, vaccinated, have comorbidities and reside in areas with higher average socioeconomic status. The 28 day cumulative incidence of hospitalization was 0.06% (95% CI: 0.02%-0.17%) among nirmatrelvir/ritonavir recipients and 0.52% (95% CI: 0.46%-0.60%) among non-recipients. For nirmatrelvir/ritonavir versus no therapy, the age-adjusted HR was 0.08 (95% CI: 0.03-0.26); the fully adjusted HR was 0.16 (95% CI: 0.05-0.50). In the machine-learning model, the primary features reducing predicted hospitalization risk were nirmatrelvir/ritonavir, younger age, vaccination, female gender and residence in a higher socioeconomic status area., Conclusions: COVID-19 hospitalization risk was reduced by 84% among nirmatrelvir/ritonavir recipients in a large, diverse healthcare system during the Omicron wave. These results suggest that nirmatrelvir/ritonavir remained highly effective in a setting substantially different than the original clinical trials., (© The Author(s) 2024. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Addressing the treatment and prevention of antibacterial-resistant gram-negative bacterial infections is a priority area of the Antibacterial Resistance Leadership Group (ARLG). The ARLG has conducted a series of observational studies to define the clinical and molecular global epidemiology of carbapenem-resistant and ceftriaxone-resistant Enterobacterales, carbapenem-resistant Pseudomonas aeruginosa, and carbapenem-resistant Acinetobacter baumannii, with the goal of optimizing the design and execution of interventional studies. One ongoing ARLG study aims to better understand the impact of fluoroquinolone-resistant gram-negative gut bacteria in neutropenic patients, which threatens to undermine the effectiveness of fluoroquinolone prophylaxis in these vulnerable patients. The ARLG has conducted pharmacokinetic studies to inform the optimal dosing of antibiotics that are important in the treatment of drug-resistant gram-negative bacteria, including oral fosfomycin, intravenous minocycline, and a combination of intravenous ceftazidime-avibactam and aztreonam. In addition, randomized clinical trials have assessed the safety and efficacy of step-down oral fosfomycin for complicated urinary tract infections and single-dose intravenous phage therapy for adult patients with cystic fibrosis who are chronically colonized with P. aeruginosa in their respiratory tract. Thus, the focus of investigation in the ARLG has evolved from improving understanding of drug-resistant gram-negative bacterial infections to positively affecting clinical care for affected patients through a combination of interventional pharmacokinetic and clinical studies, a focus that will be maintained moving forward., Competing Interests: Potential conflicts of interest. All authors report funding support from the Antibacterial Resistance Leadership Group of the National Institutes of Health (NIH) and the National Institute of Allergy and Infectious Diseases (NIAID; grant UM1AI104681). M. J. S. reports grants or contracts from Merck, bioMérieux, SNIPRBiome, and Selux Diagnostics; consulting fees from Shionogi; and participation on a data safety monitoring board (DSMB) for AbbVie. D. v. D. reports grants or contracts from Merck; consulting fees from Utility, Shionogi, Merck, Union, Roche, and Qpex; payment or honoraria from Pfizer, Entasis, and Clinical Care Options; participation on an advisory board for Universidade Federal do Rio Grande do Sul; and leadership in the British Society of Antimicrobial Chemotherapy. K. A. R. reports royalties from Springer Nature Group (textbook royalties); consulting fees, outside the submitted work, as an advisory board member for Shionogi, Qpex Biopharma/Medicines, and Utility Therapeutics and a consultant for Pulmatrix, BugsResearch, Clinartis, Spero Therapeutics, Qpex Biopharma/Medicines, Genetech, Utility Therapeutics, Venatorx, Chimerix, and Debiopharm; payment or honoraria from Shionogi (speaker bureau) and Biri Bioscience (presentation/speaker); participation on a DSMB, outside the submitted work, for Janssen Pharmaceutical; voting membership on the National Antimicrobial Susceptibility Testing Committee for the United States; and membership in the Antimicrobial Stewardship Curriculum Workgroup of the Infectious Diseases Society of America. N. R. reports grants or contracts from Merck, Sanofi, Pfizer, Quidel, and Lilly; consulting fees from Krog; payment or honoraria from Virology Education; travel support from Sanofi; participation on a DSMB or advisory board for Moderna, Sanofi, EMMES, ICON, and Seqirus; advisory roles with the Antibacterial Resistance Leadership Group, Tropical Medicine Research Center (TMRC), Centers for Disease Control and Prevention (CDC), and Pertussis Challenge; an associate editor role with Clinical Infectious Diseases; and receipt of equipment, materials, drugs, medical writing, gifts or other services from the Georgia Research Alliance. S. R. E. reports grants from the NIAID, the NIH and De Gruyter (as editor-in-chief for Statistical Communications in Infectious Diseases), the National Cancer Institute/NIH, and the CDC; royalties from Taylor & Francis; consulting fees from Genentech, AstraZeneca, Takeda, Microbiotix, Johnson & Johnson, Endologix, ChemoCentryx, Becton Dickinson, Atricure, Roviant, Neovasc, Nobel Pharma, Horizon, International Drug Development Institute, SVB Leerink, Medtronic, Regeneron, Wake Forest University, Recor, Janssen, and IDDI; payments from Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION); meeting support from the US Food and Drug Administration, Deming Conference on Applied Statistics, Clinical Trial Transformation Initiative, the Council for International Organizations of Medical Sciences, the International Chinese Statistical Association Applied Statistics Symposium, and the Antimicrobial Resistance and Stewardship Conference; and board member participation for the NIH, the Breast International Group, the University of Pennsylvania, Washington University, Duke University, Roche, Pfizer, Takeda, Akouos, Apellis, Teva, Vir, DayOneBio, Alexion, Tracon, Rakuten, AbbVie, GSK, Eli Lilly, Nuvelution, Clover, FHI Clinical, Lung Biotech, SAB Biopharm, Advantagene, Candel, Novartis, the American Statistical Association, the Society for Clinical Trials, and the Frontier Science Foundation. V. G. F. reports personal consulting fees from Novartis, Debiopharm, Genentech, Achaogen, Affinium, The Medicines Company, MedImmune, Bayer, Basilea, Affinergy, Janssen, ContraFect, Regeneron, Destiny, Amphliphi Biosciences, Integrated Biotherapeutics, C3J, Armata, Valanbio, Akagera, Aridis, Roche, and Pfizer (all paid to author); grants from the NIH, MedImmune, Allergan, Pfizer, Advanced Liquid Logics, Theravance, Novartis, Merck, Medical Biosurfaces, Locus, Affinergy, ContraFect, Karius, Genentech, Regeneron, Deep Blue, Basilea, and Janssen; royalties from UpToDate; stock options from Valanbio and ArcBio; honoraria from the Infectious Diseases Society of America for service as associate editor of Clinical Infectious Diseases; travel support from ContraFect to 2019 ECCMID; and a sepsis diagnostics patent pending. T. H. reports consulting fees from Tanabe-Mitsubishi Pharma and honoraria from Duke University and Cancer and Chemo Therapy. R. P. reports grants or contracts from ContraFect, TenNor Therapeutics Limited, BIOFIRE, and Adaptive Phage Therapeutics; a royalty-bearing know-how agreement and equity in Adaptive Phage Therapeutics through the Mayo Clinic; consulting fees from PhAST, Torus Biosystems, Day Zero Diagnostics, Mammoth Biosciences, HealthTrackRx, Netflix, Abbott Laboratories, Trellis Bioscience, Oxford Nanopore Technologies, and CARB-X; honoraria from the NBME, Up-to-Date, and the Infectious Diseases Board Review Course; a patent on Bordetella pertussis/parapertussis polymerase chain reaction issued, a patent on a device/method for sonication (with royalties paid by Samsung to Mayo Clinic), and a patent on an antibiofilm substance issued; and a financial relationship with Pathogenomix through the Mayo Clinic. N. S. reports grant funding from Duke University, the NIH, and the Antibacterial Resistance Leadership Group. R. A. B. reports grants and contracts from VenatoRx, Wockhardt, and Merck; payments from Pfizer to moderate meeting sessions; a provisional patent with Case Western Reserve University on the development of boronic acid transition state inhibitors for β-lactamases; and participation on a DSMB as a logistics associate for DMID-CROMS, Safety Oversight Committee Support, and Technical Resources International. Y. D. reports grants from Entasis and Shionogi; consulting fees from GSK, Moderna, Meiji Seika Pharma, Shionogi, Gilead, FujiFilm, and bioMérieux; and speaker payments from MSD, Shionogi, and Gilead. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Carbapenemase-producing (CP) Escherichia coli (CP-Ec) are a global public health threat. We aimed to describe the clinical and molecular epidemiology and outcomes of patients from several countries with CP-Ec isolates obtained from a prospective cohort., Methods: Patients with CP-Ec were enrolled from 26 hospitals in 6 countries. Clinical data were collected, and isolates underwent whole-genome sequencing. Clinical and molecular features and outcomes associated with isolates with or without metallo-β-lactamases (MBLs) were compared. The primary outcome was desirability of outcome ranking (DOOR) at 30 days after the index culture., Results: Of the 114 CP-Ec isolates in Consortium on resistance against carbapenems in Klebsiella and other Enterobacterales-2 (CRACKLE-2), 49 harbored an MBL, most commonly blaNDM-5 (38/49, 78%). Strong regional variations were noted with MBL-Ec predominantly found among patients in China (23/49). Clinically, MBL-Ec were more often from urine sources (49% vs 29%), less often met criteria for infection (39% vs 58%, P = .04), and had lower acuity of illness when compared with non-MBL-Ec. Among patients with infection, the probability of a better DOOR outcome for a randomly selected patient with MBL-Ec as compared with non-MBL-Ec was 62% (95% CI: 48.2-74.3%). Among infected patients, non-MBL-Ec had increased 30-day (26% vs 0%; P = .02) and 90-day (39% vs 0%; P = .001) mortality compared with MBL-Ec., Conclusions: Emergence of CP-Ec was observed with important geographic variations. Bacterial characteristics, clinical presentations, and outcomes differed between MBL-Ec and non-MBL-Ec. Mortality was higher among non-MBL isolates, which were more frequently isolated from blood, but these findings may be confounded by regional variations., Competing Interests: Potential conflicts of interest. All authors report funding support from the Antibacterial Resistance Leadership Group (ARLG) of the National Institutes of Health (NIH) and the National Institute of Allergy and Infectious Diseases (NIAID; UM1AI104681) during the conduct of this study. Additionally, during the conduct of this study, A. E. B. reports funding from the Unified Program for Therapeutics in Children (UPTiC) [1T32HD094671-01A1] from the Eunice Kennedy Shriver National institute of child health and human development. Outside of the submitted work, the authors report the following disclosures: S. S. K. reports speaker and/or advisory board payments from Pfizer, Astellas, Novartis, Merck, Menarini, and Gilead, and honoraria from UpToDate. A. E. B. reports grants or contracts from the NIH–NIAID Loan Repayment Program and Thrasher Research Foundation. B. H. reports NIH/NIAID grant K01AI148593-01 (paid to their institution). K. O. reports payments for educational events and presentations from Pfizer, MSD, and AstraZeneca; payment or honoraria from BioMerieux and Farma de Colombia; meeting support from AstraZeneca, Pfizer, MSD, and Gilead; expert testimony support from Pfizer, bioMerieux, and MSD; and payment for participation on a Data Safety and Monitoring Board (DSMB) from Pfizer. S. E. reports a Centers for Disease Control and Prevention (CDC) grant; NIH grants from the NIAID, the National Cancer Institute (NCI), and the National Heart, Lung, and Blood Institute (NHLBI); a contract with Degruter (Editor in Chief for Statistical Communications in Infectious Diseases); royalties from Taylor & Francis; consulting fees from Genentech, AstraZeneca, Takeda, Microbiotix, Johnson & Johnson, Endologix, ChemoCentryx, Becton Dickenson, Atricure, Roivant, Neovasc, Nobel Pharma, Horizon, International Drug Development Institute, SVB Leerink, Medtronic, Regeneron, and Wake Forest University (all paid to the author); honorarium payments from Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION); honoraria from the US Food and Drug Administration, the Deming Conference on Applied Statistics, and the International Chinese Statistical Association Applied Statistics Symposium; travel support from the Clinical Trial Transformation Initiative, the Council for International Organizations of Medical Sciences, and the Antimicrobial Resistance and Stewardship Conference; and Data Safety Monitoring or Advisory Board member participation for the NIH, the Breast International Group, the University of Pennsylvania, Duke University, Roche, Pfizer, Takeda, Akouos, Apellis, Teva, Vir, DayOneBio, Alexion, Tracon, Rakuten, AbbVie, GSK, Eli Lilly, Nuvelution, Clover, FHI Clinical, Lung Biotech, SAB Biopharm, Advantagene, Candel, and Novartis (all payments made to the author); and unpaid Board membership with the American Statistical Association, the Society for Clinical Trials, and the Frontier Science Foundation. R. A. B. reports grants and contracts, paid to his institution, by VenatoRx, Wockhardt, and Merck; payments made to him by Pfizer to moderate meeting sessions; a patent with Case Western Reserve University on the development of boronic acid transition state inhibitors for beta-lactamases; payment for participation on a DSMB, Safety Oversight Committee Support (SOCS), and Logistics Associate for Division of Microbiology and Infectious Diseases - Clinical Research Operations And Management Support (DMID-CROMS) (Contractor), with Technical Resources International, Inc (TRI). R. P. reports grants from BIOFIRE, ContraFect, Adaptive Phage Therapeutics, and TenNor Therapeutics Limited; is a consultant to Curetis, Specific Technologies, Abbott Laboratories, Next Gen Diagnostics, PathoQuest, Selux Diagnostics, 1928 Diagnostics, PhAST, Day Zero Diagnostics, Torus Biosystems, Mammoth Biosciences, HealthTrackRx, and Qvella, for which monies are paid to Mayo Clinic; is a consultant to Netflix and CARB-X; has a patent on Bordetella pertussis (parapertussis) polymerase chain reaction (PCR) issued, a patent on a device and method for sonication (with royalties paid by Samsung to Mayo Clinic), and a patent on an anti-biofilm substance issued; receives an editor's stipend from the Infectious Diseases Society of America (IDSA); and receives honoraria from the National Board of Medical Examiners, UpToDate, and the Infectious Diseases Board Review Course; other interests paid to her institution include Adaptive Phase Therapeutics and Pathogenomix. D. L. P. serves on the Scientific Advisory Board of the Antibiotic Action Fund and a Data Safety Monitoring or Advisory Board for Symvivo; has grant funding from Shionogi, Pfizer, and Merck; reports consulting fees (paid to the author) from Merck, Shinogi, Qpex, and Spero Therapeutics; payment or honoraria (paid to the author) for speaking engagements from Sumitomo, Merck, Pfizer, and bioMerieux; travel support from Shinogi (paid to the author); and serves on advisory boards or has given lectures for Pfizer, Merck, bioMerieux, Zuellig, Entasis, QPex, and VenatoRx. C. A. A. reports the following grants and contracts paid to his institution: NIH/NIAID 1 P01 AI152999, NIH/NIAID R01 AI148342, NIH/NIAID R01 AI134637, NIH/NIAID T32 AI141349, NIH/NIAID K24 AI121296, NIH/NIAID U19 AI144297, NIH/NIAID R01 AI150685, NIH/NIAID R21 AI151536, and support from MeMed Diagnostics Ltd, Entasis Therapeutics, Merck Pharmaceuticals, and Harris County Public Health; payments to him for UpToDate royalties; reimbursement for meeting attendance for speaking engagements from IDSA, American Society for Microbiology, Society of Hospital Epidemiology of America, European Society for Clinical Microbiology and Infectious Diseases, bioMerieux Foundation, Sociedad Argentina de Infectologia, Sociedad Chilena de Infectologia, Sociedad Colombiana de Infectologia, Panamerican Society for Infectious Diseases, and Brazilian Society for Infectious Diseases; reviewer participation as part of the NIH Grant Review Study Sections; travel expenses from the IDSA Board of Directors; honoraria as Editor-in-Chief for Antimicrobial Agents and Chemotherapy; and nonpaid participation in the World Health Organization Antibacterial Pipeline Advisory Group and the IDSA Board of Directors. H. F. C. reports royalties from serving as Senior Editor on the Sanford Guide to Antimicrobial Therapy; payment for expert testimony from Nexus Pharmaceuticals for patent litigation and from Eli Lilly for product liability; participation on a Merck DSMB for Molnuprivir paid directly to him, and stock ownership in Moderna and Merck. V. G. F. reports grants to his institution from the NIH, MedImmune, Allergan, Pfizer, Advance, Liquid Logics, Theravance, Novartis, Merck, Medical Biosurfaces, Locus, Affinergy, Contrafect, Karius, Genentech, Regeneron, Basilea, and Janssen; royalties from UpToDate; personal consulting fees from Novartis, Debiopharm, Genentech, Achaogen, Affinium, Medicines Co., MedImmune, Bayer, Basilea, Affinergy, Janssen, Contrafect, Regeneron, Destiny, Amphliphi Biosciences, Integrated Biotherapeutics, C3J, Armata, Valanbio, Akagera, Aridis, and Roche; editorial stipend from IDSA; a pending patent for a host gene expression signature diagnostic for sepsis; and stock options with Valanbio and ArcBio. D. v. D. reports grants or contracts with NIH and Merck (paid to their institution); grants or contracts with Shionogi (paid to the author); consulting fees from Actavis, Tetraphase, Sanofi-Pasteur, Medimmune, Astellas, Merck, Allergan, T2Biosystems, Roche, Achaogen, Neumedicine, Shionogi, Pfizer, Entasis, Qpex, Wellspring, Karius, Utility, and Union (all paid to the author); payment or honoraria for speaking engagements from Pfizer; and an editor's stipend from the British Society for Antimicrobial Chemotherapy., (© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: The Infectious Diseases Society of America (IDSA) is committed to providing up-to-date guidance on the treatment of antimicrobial-resistant infections. This guidance document focuses on infections caused by extended-spectrum β-lactamase producing Enterobacterales (ESBL-E), AmpC β-lactamase-producing Enterobacterales (AmpC-E), carbapenem-resistant Enterobacterales (CRE), Pseudomonas aeruginosa with difficult-to-treat resistance (DTR-P. aeruginosa), carbapenem-resistant Acinetobacter baumannii (CRAB), and Stenotrophomonas maltophilia. This updated document replaces previous versions of the guidance document., Methods: A panel of six infectious diseases specialists with expertise in managing antimicrobial-resistant infections formulated questions about the treatment of infections caused by ESBL-E, AmpC-E, CRE, DTR-P. aeruginosa, CRAB, and S. maltophilia. Because of differences in the epidemiology of resistance and availability of specific anti-infectives internationally, this document focuses on the treatment of infections in the United States., Results: Preferred and alternative suggested treatment approaches are provided with accompanying rationales, assuming the causative organism has been identified and antibiotic susceptibility results are known. Approaches to empiric treatment, transitioning to oral therapy, duration of therapy, and other management considerations are also discussed briefly. Suggested approaches apply for both adult and pediatric populations, although suggested antibiotic dosages are provided only for adults., Conclusions: The field of antimicrobial resistance is highly dynamic. Consultation with an infectious diseases specialist is recommended for the treatment of antimicrobial resistant infections. This document is current as of December 31, 2022 and will be updated periodically. The most current version of this document, including date of publication, is available at www.idsociety.org/practice-guideline/amr-guidance/., (© The Author(s) 2023. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The global burden of infection from MDR organisms (MDROs) disproportionately affects children residing in low- and middle-income countries and those with increased healthcare exposure. These populations have high rates of malnutrition making them increasingly vulnerable to infection with intestinal-derived pathogens. Malnourished children experience increased incidence of intestinal carriage and invasive infection with intestinal-derived MDROs including ESBL- and carbapenemase-producing Enterobacterales. However, the relationship between malnutrition and MDRO infection remains to be clearly defined. Impairment in intestinal barrier function and innate and adaptive immunity in malnutrition increases the risk for infection with intestinal-derived pathogens, and there is an increasing appreciation of the role of the intestinal microbiota in this process. Current evidence from human studies and animal models suggests that diet and the intestinal microbiota influence each other to determine nutritional status, with important implications for infectious outcomes. These insights are crucial to developing microbiota-targeted strategies aimed at reversing the growing burden of MDRO infections in malnourished populations worldwide., (© The Author(s) 2023. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy.)

Background: Carbapenem-resistant Klebsiella pneumoniae (CRKp) is the most prevalent carbapenem-resistant Enterobacterales in the United States. We evaluated CRKp clustering in patients in US hospitals., Methods: From April 2016 to August 2017, 350 patients with clonal group 258 CRKp were enrolled in the Consortium on Resistance Against Carbapenems in Klebsiella and other Enterobacteriaceae, a prospective, multicenter, cohort study. A maximum likelihood tree was constructed using RAxML. Static clusters shared ≤21 single-nucleotide polymorphisms (SNP) and a most recent common ancestor. Dynamic clusters incorporated SNP distance, culture timing, and rates of SNP accumulation and transmission using the R program TransCluster., Results: Most patients were admitted from home (n = 150, 43%) or long-term care facilities (n = 115, 33%). Urine (n = 149, 43%) was the most common isolation site. Overall, 55 static and 47 dynamics clusters were identified involving 210 of 350 (60%) and 194 of 350 (55%) patients, respectively. Approximately half of static clusters were identical to dynamic clusters. Static clusters consisted of 33 (60%) intrasystem and 22 (40%) intersystem clusters. Dynamic clusters consisted of 32 (68%) intrasystem and 15 (32%) intersystem clusters and had fewer SNP differences than static clusters (8 vs 9; P = .045; 95% confidence interval [CI]: -4 to 0). Dynamic intersystem clusters contained more patients than dynamic intrasystem clusters (median [interquartile range], 4 [2, 7] vs 2 [2, 2]; P = .007; 95% CI: -3 to 0)., Conclusions: Widespread intrasystem and intersystem transmission of CRKp was identified in hospitalized US patients. Use of different methods for assessing genetic similarity resulted in only minor differences in interpretation., (© The Author(s) 2022. Published by Oxford University Press on behalf of Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Nontuberculous Mycobacterium infections, particularly Mycobacterium abscessus, are increasingly common among patients with cystic fibrosis and chronic bronchiectatic lung diseases. Treatment is challenging due to intrinsic antibiotic resistance. Bacteriophage therapy represents a potentially novel approach. Relatively few active lytic phages are available and there is great variation in phage susceptibilities among M. abscessus isolates, requiring personalized phage identification., Methods: Mycobacterium isolates from 200 culture-positive patients with symptomatic disease were screened for phage susceptibilities. One or more lytic phages were identified for 55 isolates. Phages were administered intravenously, by aerosolization, or both to 20 patients on a compassionate use basis and patients were monitored for adverse reactions, clinical and microbiologic responses, the emergence of phage resistance, and phage neutralization in serum, sputum, or bronchoalveolar lavage fluid., Results: No adverse reactions attributed to therapy were seen in any patient regardless of the pathogen, phages administered, or the route of delivery. Favorable clinical or microbiological responses were observed in 11 patients. Neutralizing antibodies were identified in serum after initiation of phage delivery intravenously in 8 patients, potentially contributing to lack of treatment response in 4 cases, but were not consistently associated with unfavorable responses in others. Eleven patients were treated with only a single phage, and no phage resistance was observed in any of these., Conclusions: Phage treatment of Mycobacterium infections is challenging due to the limited repertoire of therapeutically useful phages, but favorable clinical outcomes in patients lacking any other treatment options support continued development of adjunctive phage therapy for some mycobacterial infections., Competing Interests: Potential conflicts of interest. G. F. H. is a consultant for and receives grant support not directly related to this work from Janssen Pharmaceuticals (Collaborative Research Agreement); reports consulting fees from Janssen Inc and Tessera Inc; and reports presentation honoraria from the Pittsburgh Foundation and a leadership or fiduciary role with the Charles E. Kaufman Foundation scientific advisory board. R. M. De. and G. F. H. are co-inventors on patent applications related to the use of phages for treating nontuberculous mycobacterial (NTM) infections filed by the University of Pittsburgh of the Commonwealth System of Higher Education. D. v. D. is a consultant for Actavis, Tetraphase, Sanofi Pasteur, MedImmune, Astellas, Merck, Allergan, T2Biosystems, Roche, Achaogen, Neumedicine, Shionogi, Pfizer, Entasis, QPex, Wellspring, Karius, Melinta, and Utility; receives an editor’s stipend from British Society for Antimicrobial Chemotherapy; has received funding for unrelated projects from NIH, Merck, and Shionogi; reports payments for lectures, presentations, speaker’s bureaus, manuscript writing, or educational events from Pfizer and Entasis; reports paid participation on a data and safety monitoring board (DSMB) or advisory board for Utility, Union, Entasis, and Merck; and reports a paid leadership or fiduciary role with the British Society for Antimicrobial Chemotherapy. K. A. C. has received consulting fees from Insmed (clinical trial site), Hillrom (clinical trial site), Paratek, Microbion, and AN2, and reports honoraria for a presentation from Insmed. G. H. receives grant support unrelated to this study from Karius, Allovir, and AstraZeneca, and reports participation on a DSMB or advisory board with Karius. R. T. S. is a paid consultant to Vir Biotechnology and to LysNtech; holds stock options in Antiva Biosciences and CytoDyn and stock or stock options with NoniGenex and Arcturus; previously served as an uncompensated member of the AmpliPhi scientific advisory board; reports grants or contracts paid to institution from the National Institute of Allergy and Infectious Diseases; reports consulting fees from Pfizer, Sempra Energy, and Nurix; has patents planned, issued, or pending for orally bioavailable anti-coronavirus compounds; reports paid participation on DSMBs or advisory boards for Merck, VIr Biosciences, SNIPR Biome, and Pardes Biosciences; and holds leadership or fiduciary roles with the International Antiviral Society (IAS)–USA and Specialists in Global Health. C. A. B. reports contracts to institution for clinical trials from Gilead and DNAe; payment to author for educational lectures from IAS-USA, Practice Point Communications (Optimal Management of HIV Disease and Hepatitis Clinical Conference [OPMAN] conference), and University of Arizona; has received payment for travel to the OPMAN conference from Practice Point Communications; served on a DSMB for ViiV/GlaxoSmith Kline; has held unpaid volunteer roles with IAS-USA and the Conference on Retroviruses and Opportunistic Infections Foundation Board; and has served as Deputy Editor/Associate Editor for the Infectious Diseases Society of America. A. K. reports the following grants or contracts unrelated to this work: National Health and Medical Research Council (NHMRC, Australia) Investigator Grant at Emerging Leadership 1 level, Conquer CF, Innovation Grant from Cystic Fibrosis Australia, Research Establishment Fellowship from the Royal Australasian College of Physicians and Research Award from the Australasian Society for Infectious Diseases (all paid to institution); payment to institution for grant application review for the Italian Cystic Fibrosis Research Foundation; unpaid role as member of DSMB for FluBubs (Safety and Immunogenicity of Early Quadrivalent Influenza Vaccine); unpaid leadership or fiduciary roles as Deputy Director (Clinical) of Phage Australia, pediatric infectious diseases research representative on the Australian Society for Infectious Diseases Clinical Research Network Steering Committee and the Australia and New Zealand Paediatric Infectious Diseases Group Executive Committee, member of the Sydney Children’s Hospitals Network Human Research Ethics Committee Scientific Advisory Committee, and member of the Sydney Children’s Hospitals Network Advanced Therapeutics Steering Committee. A. W. B. reports a role as a part-time employee of the Cystic Fibrosis Foundation, which provides some grant support to G. F. H.’s laboratory and, for the purposes of this manuscript, is the treating physician of one of the NTM patients in the cystic fibrosis clinic at Inova Fairfax Hospital. C. B. G. reports consulting fees from Advisory Janssen. B. J. M. reports an NHMRC Investigator Grant and philanthropic grant from the Curing Homesickness Foundation, both paid to institution and unrelated to this work; unpaid participation as member of the DSMB for the PATRIC trial; and unpaid position as board director of the Australasian Society for Infectious Diseases. M. G. T. O. reports a Cystic Fibrosis Foundation Adult Center Award and Cystic Fibrosis Foundation Therapeutic Development Center Award, unrelated to this work; support for attending meetings and/or travel, paid to University of Miami, from the Cystic Fibrosis Foundation Adult Center Award for attending North American Cystic Fibrosis Conference and a Cystic Fibrosis Foundation Therapeutic Development Center Award for attending the Therapeutics Development Network spring meeting; and an unpaid position as Cystic Fibrosis Lifestyle Foundation board member. J. I. reports an Investigator Grant (personal support) unrelated to this work from NHMRC. A. M. reports consulting fees paid to author as a member of the Air Liquide Advisory Board. J. A. N. reports contracts or grants unrelated to this work from the Cystic Fibrosis Foundation. M. S. reports funding on a project to set up a phage therapy laboratory in Finland, unrelated to this work, from the Jane and Aatos Erkko Foundation. P. W. reports consulting fees from AstraZeneca, GlaxoSmithKline, Pfizer, Sanofi Regeneron, and Vertex; payment or honoraria for lectures, presentations, speaker’s bureaus, manuscript writing, or educational events from AstraZeneca, GlaxoSmithKline, Pfizer, Boehringer Ingelheim, and Vertex; and a leadership or fiduciary role with the Cystic Fibrosis Australia National Asthma Council of Australia. D. E. M. reports stock or stock options (no payments) with Moderna (1 share) and Pfizer (5 shares). R. M. Da. reports grants from the NIH unrelated to this work (grant number K01-AI125726 [principal investigator]). All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Infectious Diseases Society of America.)

Background: Community-acquired carbapenem-resistant Enterobacterales (CA-CRE) are an important threat., Methods: In CRACKLE-2, we defined patients with CA-CRE as admitted from home, without pre-existing conditions, and a positive culture within 48 h of admission. Healthcare-associated CRE (HA-CRE) were those with the lowest likelihood of community acquisition, not admitted from home and cultured &gt;48 h after admission. Specific genetic markers in carbapenemase-producing Klebsiella pneumoniae were evaluated through random forest modelling., Results: CA-CRE and HA-CRE were detected in 83 (10%) and 208 (26%) of 807 patients. No significant differences were observed in bacterial species or strain type distribution. K. pneumoniae (204/291, 70%) was the most common CRE species, of these 184/204 (90%) were carbapenemase producers (CPKP). The top three genetic markers in random forest models were kpi&#95;SA15, fimE, and kpfC. Of these, kpi&#95;SA15 (which encodes a chaperone/usher system) was positively associated (OR 3.14, 95% CI 1.13-8.87, P = 0.026), and kpfC negatively associated (OR 0.21, 95% CI 0.05-0.72, P = 0.015) with CA-CPKP., Conclusions: Ten percent of CDC-defined CRE were CA. The true proportion of CA-CRE in hospitalized patients is likely lower as patients may have had unrecorded prior healthcare exposure. The kpi&#95;SA15 operon was associated with the CA phenotype., (© The Author(s) 2022. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The term difficult-to-treat resistance has been recently coined to identify Gram-negative bacteria exhibiting resistance to all fluoroquinolones and all β-lactam categories, including carbapenems. Such bacteria are posing serious challenges to clinicians trying to identify the best therapeutic option for any given patient. Delayed appropriate therapy has been associated with worse outcomes including increase in length of stay, increase in total in-hospital costs and ∼20% increase in the risk of in-hospital mortality. In addition, time to appropriate antibiotic therapy has been shown to be an independent predictor of 30 day mortality in patients with resistant organisms. Improving and anticipating aetiological diagnosis through optimizing not only the identification of phenotypic resistance to antibiotic classes/agents, but also the identification of specific resistance mechanisms, would have a major impact on reducing the frequency and duration of inappropriate early antibiotic therapy. In light of these considerations, the present paper reviews the increasing need for rapid diagnosis of bacterial infections and efficient laboratory workflows to confirm diagnoses and facilitate prompt de-escalation to targeted therapy, in line with antimicrobial stewardship principles. Rapid diagnostic tests currently available and future perspectives for their use are discussed. Early appropriate diagnostics and treatment of MDR Gram-negative infections require a multidisciplinary approach that includes multiple different diagnostic methods and further consensus of algorithms, protocols and guidelines to select the optimal antibiotic therapy., (© The Author(s) 2022. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy.)

Background: The Infectious Diseases Society of America (IDSA) is committed to providing up-to-date guidance on the treatment of antimicrobial-resistant infections. The initial guidance document on infections caused by extended-spectrum β-lactamase producing Enterobacterales (ESBL-E), carbapenem-resistant Enterobacterales (CRE), and Pseudomonas aeruginosa with difficult-to-treat resistance (DTR-P. aeruginosa) was published on 17 September 2020. Over the past year, there have been a number of important publications furthering our understanding of the management of ESBL-E, CRE, and DTR-P. aeruginosa infections, prompting a rereview of the literature and this updated guidance document., Methods: A panel of 6 infectious diseases specialists with expertise in managing antimicrobial-resistant infections reviewed, updated, and expanded previously developed questions and recommendations about the treatment of ESBL-E, CRE, and DTR-P. aeruginosa infections. Because of differences in the epidemiology of resistance and availability of specific anti-infectives internationally, this document focuses on the treatment of infections in the United States., Results: Preferred and alternative treatment recommendations are provided with accompanying rationales, assuming the causative organism has been identified and antibiotic susceptibility results are known. Approaches to empiric treatment, duration of therapy, and other management considerations are also discussed briefly. Recommendations apply for both adult and pediatric populations., Conclusions: The field of antimicrobial resistance is highly dynamic. Consultation with an infectious diseases specialist is recommended for the treatment of antimicrobial-resistant infections. This document is current as of 24 October 2021. The most current versions of IDSA documents, including dates of publication, are available at www.idsociety.org/practice-guideline/amr-guidance/., Competing Interests: Potential conflicts of interest. The following list is a reflection of what has been reported to IDSA. To provide thorough transparency, IDSA requires full disclosure of all relationships, regardless of relevancy to the guidance topic. Evaluation of such relationships as potential conflicts of interest is determined by a review process which includes assessment by the Board of Directors liaison to the Standards and Practice Guidelines Committee and, if necessary, the Conflicts of Interest and Ethics Committee. The assessment of disclosed relationships for possible conflicts of interests is based on the relative weight of the financial relationship (ie, monetary amount) and the relevance of the relationship (ie, the degree to which an association might reasonably be interpreted by an independent observer as related to the topic or recommendation of consideration). Readers of this guidance should be mindful of this when the list of disclosures is reviewed. P. D. T. has nothing to disclose and does not receive any funding from any commercial groups. S. L. A. serves as advisor to Shionogi and Entasis Therapeutics; served on the advisory panel for Merck, Paratek, Medicines Company, Zavante, Shionogi, Sempra, and Theravance; and received research funding paid from Melinta and Merck. R. A. B. receives research funding from the National Institute of Allergy and Infectious Diseases, Veterans Health Administration, Shionogi, VenatoRx, Merck, Allecra, Wockhardt, Shionogi, AstraZeneca, Harrington Foundation, and Entasis; received research funding from Tetraphase and Steris; and served on the editorial boards for Antimicrobial Agents and Chemotherapy, mBio, and the Veterans Affairs Society for Prevention of Infectious Diseases. A. J. M. serves as a consultant/advisor for Merck, Shionogi, Qpex Biopharma, Accelerate Diagnostics, and VenatoRX; received research grants from the CDC and Wallace H. Coulter Endowment; and served as an advisor for Rempex and Antimicrobial Resistance Services. D. v. D. serves as member of the advisory group for Qpex Biopharma, Shionogi, and Merck; receives honoraria from Shionogi and Pfizer; receives other remuneration from the British Society for Antimicrobial Chemotherapy; receives research grants from Shionogi; served as an advisory board member for Entasis, Roche, Allergan, Utility, and Achaogen; served as non-promotional speaker for Entasis and Pfizer; received research funding from the National Institutes of Health and Merck; serves as editor-in-chief for JAC-Antimicrobial Resistance; and is on the program committee for the European Society of Clinical Microbiology and Infectious Diseases. C. J. C. served on the advisory board for Merck, Qpex Biopharma, and Shionogi; serves as an advisory Board member for Astellas, Cidara, and Scynexis; serves as a consultant for Needham & Associates; and receives research funding from Astellas and Merck. All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Background: Multidrug-resistant Enterobacterales (MDR-E) are important pathogens. People living with human immunodeficiency virus (HIV; PLWH) may be at greater risk for MDR-E infection given relatively high antibiotic exposure and burden of comorbidities., Methods: We analyzed data from 36 521 patients in a healthcare system in North Carolina who had a clinical culture with growth of an Enterobacterales species from 2000 to 2018; 440 were PLWH. We used generalized linear models to estimate prevalence ratios and differences, contrasting PLWH and people not living with HIV (PNLWH) for resistance to individual antibiotic classes, as well as MDR-E. We assessed trends in prevalence over time by calculating the 5-year moving average and fitting restricted cubic spline models., Results: The overall prevalence of MDR-E was higher among PLWH (21.5%; 95% confidence interval [CI], 18.2%-25.1%) vs PNLWH (16.5%; 95% CI, 16.2%-16.9%), with an adjusted prevalence ratio of 1.38 (95% CI, 1.14-1.65). PLWH had higher rates of antimicrobial resistance than PNLWH for all antibiotic classes analyzed, including penicillins, penicillin/beta lactamase inhibitor combinations, and sulfonamides. MDR-E prevalence was 3 to 10 percentage points higher among PLWH than PNLWH throughout the study period based on the 5-year moving average., Conclusions: In a large clinical study population in the southeastern United States from 2000 to 2018, the prevalence of antibacterial resistance among Enterobacterales was consistently higher among PLWH than PNLWH. These data highlight the importance of identifying and mitigating the factors that contribute to antimicrobial resistance in PLWH, given the potential clinical consequences of these resistant pathogens., (© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Background: People with HIV (PWH) may be at increased risk for MDR Enterobacterales (MDR-E) infection or colonization, relative to individuals without HIV, due to a greater burden of comorbidities as well as HIV-related intestinal inflammation and microbiota alterations., Objectives: To characterize antibiotic susceptibility of enteric Enterobacterales and risk factors for antimicrobial-resistant bacterial infections in a sample of PWH attending routine clinic visits., Methods: Participants provided self-administered rectal swabs and completed questionnaires regarding healthcare, travel and occupational exposures for the prior 12 months. Rectal samples were processed to identify Enterobacterales species, and susceptibility testing was performed., Results: Among 82 participants, 110 Enterobacterales isolates were obtained. Non-susceptibility was common for penicillins, sulphonamides and first-generation cephalosporins. MDR-E was present in 20% of participants. HIV-related characteristics, including current or nadir CD4 cell count, viral suppression, or AIDS-defining clinical conditions, were not associated with MDR-E., Conclusions: MDR-E colonization is common in this population of PWH. Further research evaluating risk factors for MDR-E in PWH may inform infection prevention approaches to better protect at-risk populations from these difficult-to-treat infections., (Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy 2022.)

The Infectious Diseases Society of America (IDSA) is committed to providing up-to-date guidance on the treatment of antimicrobial-resistant infections. A previous guidance document focused on infections caused by extended-spectrum β-lactamase-producing Enterobacterales (ESBL-E), carbapenem-resistant Enterobacterales (CRE), and Pseudomonas aeruginosa with difficult-to-treat resistance (DTR-P. aeruginosa). Here, guidance is provided for treating AmpC β-lactamase-producing Enterobacterales (AmpC-E), carbapenem-resistant Acinetobacter baumannii (CRAB), and Stenotrophomonas maltophilia infections. A panel of 6 infectious diseases specialists with expertise in managing antimicrobial-resistant infections formulated questions about the treatment of AmpC-E, CRAB, and S. maltophilia infections. Answers are presented as suggested approaches and corresponding rationales. In contrast to guidance in the previous document, published data on the optimal treatment of AmpC-E, CRAB, and S. maltophilia infections are limited. As such, guidance in this document is provided as "suggested approaches" based on clinical experience, expert opinion, and a review of the available literature. Because of differences in the epidemiology of resistance and availability of specific anti-infectives internationally, this document focuses on the treatment of infections in the United States. Preferred and alternative treatment suggestions are provided, assuming the causative organism has been identified and antibiotic susceptibility results are known. Approaches to empiric treatment, duration of therapy, and other management considerations are also discussed briefly. Suggestions apply for both adult and pediatric populations. The field of antimicrobial resistance is highly dynamic. Consultation with an infectious diseases specialist is recommended for the treatment of antimicrobial-resistant infections. This document is current as of 17 September 2021 and will be updated annually. The most current version of this document, including date of publication, is available at www.idsociety.org/practice-guideline/amr-guidance-2.0/., (© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Stenotrophomonas maltophilia is a non-fermenting, Gram-negative bacillus that has emerged as an opportunistic nosocomial pathogen. Its intrinsic multidrug resistance makes treating infections caused by S. maltophilia a great clinical challenge. Clinical management is further complicated by its molecular heterogeneity that is reflected in the uneven distribution of antibiotic resistance and virulence determinants among different strains, the shortcomings of available antimicrobial susceptibility tests and the lack of standardized breakpoints for the handful of antibiotics with in vitro activity against this microorganism. Herein, we provide an update on the most recent literature concerning these issues, emphasizing the impact they have on clinical management of S. maltophilia infections., (Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy 2022.)

Introduction: Most studies of solid organ transplant (SOT) recipients with COVID-19 focus on outcomes within one month of illness onset. Delayed mortality in SOT recipients hospitalized for COVID-19 has not been fully examined., Methods: We used data from a multicenter registry to calculate mortality by 90 days following initial SARS-CoV-2 detection in SOT recipients hospitalized for COVID-19 and developed multivariable Cox proportional-hazards models to compare risk factors for death by days 28 and 90., Results: Vital status at day 90 was available for 936 of 1117 (84%) SOT recipients hospitalized for COVID-19: 190 of 936 (20%) died by 28 days and an additional 56 of 246 deaths (23%) occurred between days 29 and 90. Factors associated with mortality by day 90 included: age > 65 years [aHR 1.8 (1.3-2.4), p =<0.001], lung transplant (vs. non-lung transplant) [aHR 1.5 (1.0-2.3), p=0.05], heart failure [aHR 1.9 (1.2-2.9), p=0.006], chronic lung disease [aHR 2.3 (1.5-3.6), p<0.001] and body mass index ≥ 30 kg/m 2 [aHR 1.5 (1.1-2.0), p=0.02]. These associations were similar for mortality by day 28. Compared to diagnosis during early 2020 (March 1-June 19, 2020), diagnosis during late 2020 (June 20-December 31, 2020) was associated with lower mortality by day 28 [aHR 0.7 (0.5-1.0, p=0.04] but not by day 90 [aHR 0.9 (0.7-1.3), p=0.61]., Conclusions: In SOT recipients hospitalized for COVID-19, >20% of deaths occurred between 28 and 90 days following SARS-CoV-2 diagnosis. Future investigations should consider extending follow-up duration to 90 days for more complete mortality assessment., (© The Author(s) 2022. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Treatment options for Achromobacter xylosoxidans are limited. Eight cystic fibrosis patients with A. xylosoxidans were treated with 12 cefiderocol courses. Pretreatment in vitro resistance was seen in 3 of 8 cases. Clinical response occurred after 11 of 12 treatment courses. However, microbiologic relapse was observed after 11 of 12 treatment courses, notably without emergence of resistance., (© The Author(s) 2020. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Background: Persons with human immunodeficiency virus (PWH) with persistently low CD4 counts despite efficacious antiretroviral therapy could have higher hospitalization risk., Methods: In 6 US and Canadian clinical cohorts, PWH with virologic suppression for ≥1 year in 2005-2015 were followed until virologic failure, loss to follow-up, death, or study end. Stratified by early (years 2-5) and long-term (years 6-11) suppression and lowest presuppression CD4 count <200 and ≥200 cells/µL, Poisson regression models estimated hospitalization incidence rate ratios (aIRRs) comparing patients by time-updated CD4 count category, adjusted for cohort, age, gender, calendar year, suppression duration, and lowest presuppression CD4 count., Results: The 6997 included patients (19 980 person-years) were 81% cisgender men and 40% white. Among patients with lowest presuppression CD4 count <200 cells/μL (44%), patients with current CD4 count 200-350 vs >500 cells/μL had aIRRs of 1.44 during early suppression (95% confidence interval [CI], 1.01-2.06), and 1.67 (95% CI, 1.03-2.72) during long-term suppression. Among patients with lowest presuppression CD4 count ≥200 (56%), patients with current CD4 351-500 vs >500 cells/μL had an aIRR of 1.22 (95% CI, .93-1.60) during early suppression and 2.09 (95% CI, 1.18-3.70) during long-term suppression., Conclusions: Virologically suppressed patients with lower CD4 counts experienced higher hospitalization rates and could potentially benefit from targeted clinical management strategies., (© The Author(s) 2020. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

In December 2019, the Antibacterial Resistance Leadership Group (ARLG) was awarded funding for another 7-year cycle to support a clinical research network on antibacterial resistance. ARLG 2.0 has 3 overarching research priorities: infections caused by antibiotic-resistant (AR) gram-negative bacteria, infections caused by AR gram-positive bacteria, and diagnostic tests to optimize use of antibiotics. To support the next generation of AR researchers, the ARLG offers 3 mentoring opportunities: the ARLG Fellowship, Early Stage Investigator seed grants, and the Trialists in Training Program. The purpose of this article is to update the scientific community on the progress made in the original funding period and to encourage submission of clinical research that addresses 1 or more of the research priority areas of ARLG 2.0., (© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Background: To assess the possible impact of antiretroviral therapy improvements, aging, and comorbidities, we examined trends in all-cause and cause-specific hospitalization rates among persons with HIV (PWH) from 2005 to 2015., Methods: In 6 clinical cohorts, we followed PWH in care (≥1 outpatient CD4 count or HIV load [VL] every 12 months) and categorized ICD codes of primary discharge diagnoses using modified Clinical Classifications Software. Poisson regression estimated hospitalization rate ratios for calendar time trends, adjusted for demographics, HIV risk factor, and annually updated age, CD4, and VL., Results: Among 28 057 patients (125 724 person-years), from 2005 to 2015, the median CD4 increased from 389 to 580 cells/µL and virologic suppression from 55% to 85% of patients. Unadjusted all-cause hospitalization rates decreased from 22.3 per 100 person-years in 2005 (95% confidence interval [CI], 20.6-24.1) to 13.0 in 2015 (95% CI, 12.2-14.0). Unadjusted rates decreased for almost all diagnostic categories. Adjusted rates decreased for all-cause, cardiovascular, and AIDS-defining conditions, increased for non-AIDS-defining infection, and were stable for most other categories., Conclusions: Among PWH with increasing CD4 counts and viral suppression, unadjusted hospitalization rates decreased for all-cause and most cause-specific hospitalizations, despite the potential effects of aging, comorbidities, and cumulative exposure to HIV and antiretrovirals., (Published by Oxford University Press for the Infectious Diseases Society of America 2020.)

Background: Antimicrobial-resistant infections are commonly encountered in US hospitals and result in significant morbidity and mortality. This guidance document provides recommendations for the treatment of infections caused by extended-spectrum β-lactamase-producing Enterobacterales (ESBL-E), carbapenem-resistant Enterobacterales (CRE), and Pseudomonas aeruginosa with difficult-to-treat resistance (DTR-P. aeruginosa)., Methods: A panel of 6 infectious diseases specialists with expertise in managing antimicrobial-resistant infections formulated common questions regarding the treatment of ESBL-E, CRE, and DTR-P. aeruginosa infections. Based on review of the published literature and clinical experience, the panel provide recommendations and associated rationale for each recommendation. Because of significant differences in the molecular epidemiology of resistance and the availability of specific anti-infective agents globally, this document focuses on treatment of antimicrobial-resistant infections in the United States., Results: Approaches to empiric treatment selection, duration of therapy, and other management considerations are briefly discussed. The majority of guidance focuses on preferred and alternative treatment recommendations for antimicrobial-resistant infections, assuming that the causative organism has been identified and antibiotic susceptibility testing results are known. Treatment recommendations apply to both adults and children., Conclusions: The field of antimicrobial resistance is dynamic and rapidly evolving, and the treatment of antimicrobial-resistant infections will continue to challenge clinicians. This guidance document is current as of 17 September 2020. Updates to this guidance document will occur periodically as new data emerge. Furthermore, the panel will expand recommendations to include other problematic gram-negative pathogens in future versions. The most current version of the guidance including the date of publication can be found at www.idsociety.org/practice-guideline/amr-guidance/., (© The Author(s) 2020. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Background: Antimicrobial-resistant infections are commonly encountered in US hospitals and result in significant morbidity and mortality. This guidance document provides recommendations for the treatment of infections caused by extended-spectrum β-lactamase-producing Enterobacterales (ESBL-E), carbapenem-resistant Enterobacterales (CRE), and Pseudomonas aeruginosa with difficult-to-treat resistance (DTR-P. aeruginosa)., Methods: A panel of 6 infectious diseases specialists with expertise in managing antimicrobial-resistant infections formulated common questions regarding the treatment of ESBL-E, CRE, and DTR-P. aeruginosa infections. Based on review of the published literature and clinical experience, the panel provide recommendations and associated rationale for each recommendation. Because of significant differences in the molecular epidemiology of resistance and the availability of specific anti-infective agents globally, this document focuses on treatment of antimicrobial-resistant infections in the United States., Results: Approaches to empiric treatment selection, duration of therapy, and other management considerations are briefly discussed. The majority of guidance focuses on preferred and alternative treatment recommendations for antimicrobial-resistant infections, assuming that the causative organism has been identified and antibiotic susceptibility testing results are known. Treatment recommendations apply to both adults and children., Conclusions: The field of antimicrobial resistance is dynamic and rapidly evolving, and the treatment of antimicrobial-resistant infections will continue to challenge clinicians. This guidance document is current as of 17 September 2020. Updates to this guidance document will occur periodically as new data emerge. Furthermore, the panel will expand recommendations to include other problematic gram-negative pathogens in future versions. The most current version of the guidance including the date of publication can be found at www.idsociety.org/practice-guideline/amr-guidance/., (© The Author(s) 2021. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Daptomycin (DAP) is key in treating multidrug-resistant Staphylococcus infections. Diminished susceptibility to DAP is emerging among Staphylococcus epidermidis strains although mechanisms for non-susceptibility (NS) remain poorly understood. We report a case of persistent S. epidermidis bacteremia in which loss of DAP susceptibility arose during prolonged treatment. Whole genome sequencing identified two mutations, Q371del and P415L, in a single-affected gene, WalK , that coincided with the emergence of DAP-NS. Protein modeling of the mutations predicted a disruption of WalK protein configuration. The emergence of mutations in a single-gene during DAP exposure raises concerns in an era of increasingly treatment-resistant infections. Lay summary: Daptomycin is an important antibiotic for fighting Staphylococcus infections. We identified variants in the WalK gene that were coincident with resistance in a clinical Staphylococcus epidermidis infection. Clinicians, hospital epidemiologists, and microbiology laboratories need to be aware of the potential for the evolution of drug resistance during prolonged daptomycin therapy., (© The Author(s) 2020. Published by Oxford University Press on behalf of the Foundation for Evolution, Medicine, and Public Health.)

The coronavirus disease 2019 (COVID-19) pandemic is having an enormous impact on public health. Infection with SARS-CoV-2 has become a leading cause of morbidity and mortality in many regions around the world. As many COVID-19 patients are treated with antibiotics, there is concern regarding an associated rise in rates of antimicrobial resistance (AMR). On the other hand, social distancing, isolation and reduced travel may result in decreased spread of AMR. In this issue of JAC-Antimicrobial Resistance , we present a PRO/CON debate on the question of the potential impact of COVID-19 on AMR rates., (© The Author(s) 2020. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy.)

Treatment options for multidrug-resistant (MDR) gram-negative infection are growing. However, postregistration, pragmatic, and clinician-led clinical trials in this field are few, recruit small sample sizes, and experience deficiencies in design and operations. MDR gram-negative therapeutic trials are often inefficient, only evaluating a single antibiotic or strategy at a time. Novel clinical trial designs offer potential solutions by attempting to obtain clinically meaningful conclusions at the end or during a trial, for many treatment strategies, simultaneously. An integrated, consensus approach to MDR gram-negative infection trial design is crucial., (© The Author(s) 2019. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Background: Predicting mortality risk in patients is important in research settings. The Pitt bacteremia score (PBS) is commonly used as a predictor of early mortality risk in patients with bloodstream infections (BSIs). We determined whether the PBS predicts 14-day inpatient mortality in nonbacteremia carbapenem-resistant Enterobacteriaceae (CRE) infections., Methods: Patients were selected from the Consortium on Resistance Against Carbapenems in Klebsiella and Other Enterobacteriaceae, a prospective, multicenter, observational study. We estimated risk ratios to analyze the predictive ability of the PBS overall and each of its components individually. We analyzed each component of the PBS in the prediction of mortality, assessed the appropriate cutoff value for the dichotomized score, and compared the predictive ability of the qPitt score to that of the PBS., Results: In a cohort of 475 patients with CRE infections, a PBS ≥4 was associated with mortality in patients with nonbacteremia infections (risk ratio [RR], 21.9; 95% confidence interval [CI], 7.0, 68.8) and with BSIs (RR, 6.0; 95% CI, 2.5, 14.4). In multivariable analysis, the hypotension, mechanical ventilation, mental status, and cardiac arrest parameters of the PBS were independent risk factors for 14-day all-cause inpatient mortality. The temperature parameter as originally calculated for the PBS was not independently associated with mortality. However, a temperature <36.0°C vs ≥36°C was independently associated with mortality. A qPitt score ≥2 had similar discrimination as a PBS ≥4 in nonbacteremia infections., Conclusions: Here, we validated that the PBS and qPitt score can be used as reliable predictors of mortality in nonbacteremia CRE infections., (© The Author(s) 2019. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Patient management is not based on a single decision. Rather, it is dynamic: based on a sequence of decisions, with therapeutic adjustments made over time. Adjustments are personalized: tailored to individual patients as new information becomes available. However, strategies allowing for such adjustments are infrequently studied. Traditional antibiotic trials are often nonpragmatic, comparing drugs for definitive therapy when drug susceptibilities are known. COMparing Personalized Antibiotic StrategieS (COMPASS) is a trial design that compares strategies consistent with clinical practice. Strategies are decision rules that guide empiric and definitive therapy decisions. Sequential, multiple-assignment, randomized (SMART) COMPASS allows evaluation when there are multiple, definitive therapy options. SMART COMPASS is pragmatic, mirroring clinical, antibiotic-treatment decision-making and addressing the most relevant issue for treating patients: identification of the patient-management strategy that optimizes the ultimate patient outcomes. SMART COMPASS is valuable in the setting of antibiotic resistance, when therapeutic adjustments may be necessary due to resistance., (© The Author(s) 2018. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

A strong synergy can result from China-US antimicrobial resistance (AMR) collaborations given similarities and differences between their respective healthcare systems and research infrastructures. The Antibacterial Resistance Leadership Group has employed a model of realistic growth, starting with a feasible, relatively low-resource observational study in a critical priority pathogen. This and other observational studies will provide vital scientific information required for the rational design of future interventional trials. In addition, it provides a mutual, low-risk opportunity for determining the strengths and opportunities of the research collaboration. Issues identified during the observational studies can be addressed prior to the initiation of high-resource interventional studies. Collaborative clinical AMR studies between China and the United States have tremendous potential to decrease AMR rates, improve responsible antibiotic use, and ultimately improve the lives of patients in both countries.

Background: The efficacy of ceftazidime-avibactam-a cephalosporin-β-lactamase inhibitor combination with in vitro activity against Klebsiella pneumoniae carbapenemase-producing carbapenem-resistant Enterobacteriaceae (CRE)-compared with colistin remains unknown., Methods: Patients initially treated with either ceftazidime-avibactam or colistin for CRE infections were selected from the Consortium on Resistance Against Carbapenems in Klebsiella and other Enterobacteriaceae (CRACKLE), a prospective, multicenter, observational study. Efficacy, safety, and benefit-risk analyses were performed using intent-to-treat analyses with partial credit and the desirability of outcome ranking approaches. The ordinal efficacy outcome was based on disposition at day 30 after starting treatment (home vs not home but not observed to die in the hospital vs hospital death). All analyses were adjusted for confounding using inverse probability of treatment weighting (IPTW)., Results: Thirty-eight patients were treated first with ceftazidime-avibactam and 99 with colistin. Most patients received additional anti-CRE agents as part of their treatment. Bloodstream (n = 63; 46%) and respiratory (n = 30; 22%) infections were most common. In patients treated with ceftazidime-avibactam versus colistin, IPTW-adjusted all-cause hospital mortality 30 days after starting treatment was 9% versus 32%, respectively (difference, 23%; 95% bootstrap confidence interval, 9%-35%; P = .001). In an analysis of disposition at 30 days, patients treated with ceftazidime-avibactam, compared with those treated within colistin, had an IPTW-adjusted probability of a better outcome of 64% (95% confidence interval, 57%-71%). Partial credit analyses indicated uniform superiority of ceftazidime-avibactam to colistin., Conclusions: Ceftazidime-avibactam may be a reasonable alternative to colistin in the treatment of K. pneumoniae carbapenemase-producing CRE infections. These findings require confirmation in a randomized controlled trial., (© The Author 2017. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Patients who are admitted to the hospital after sustaining a large burn injury are at high risk for developing hospital-associated infections. If patients survive the initial 72 hours after a burn injury, infections are the most common cause of death. Ventilator-associated pneumonia is the most important infection in this patient population. The risk of infections caused by multidrug-resistant bacterial pathogens increases with hospital length of stay in burn patients. In the first days of the postburn hospitalization, more susceptible, Gram-positive organisms predominate, whereas later more resistant Gram-negative organisms are found. These findings impact the choice of empiric antibiotics in critically ill burn patients. A proactive infection control approach is essential in burn units. Furthermore, a multidisciplinary approach to burn patients with a team that includes an infectious disease specialist and a pharmacist in addition to the burn surgeon is highly recommended., (© The Author 2017. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Enrolling severely burn injured patients into prospective research studies poses specific challenges to investigators. The authors describe their experience of recruiting adults with ≥20% TBSA burns or inhalation injury admitted to a single academic burn unit into observational research with minimally invasive specimen collection. The authors outline iterative changes that they made to their recruitment processes in response to perceived weaknesses leading to delays in enrollment. The primary outcome was the change in days to consent for enrolled patients or cessation of recruitment for nonenrolled patients before and after the interventional modifications. The authors assessed change in overall enrollment as a secondary outcome. Study enrollment was approximately 70% in both 4-month study periods before and after the intervention. Following the intervention, time to consent by surrogate decision maker decreased from a median of 26.5 days (interquartile range [IQR] 14-41) to 3 days (IQR 3-6) (P = .004). Time to initial consent by patient changed from a median of 15 days (IQR 2-30) to 3 days (IQR 2-6) (P = .27). Time to decline for nonenrolled patients decreased from a median of 12 days (IQR 6.5-27) to 1.5 days (IQR 1-3.5) (P = .026). Both the findings of the study and a brief literature review suggest that careful design of the recruitment protocol, increased experience of the study team, and broad time windows for both approach and enrollment improve the efficiency of recruiting critically injured burn patients into research.

Classic determinants of burn mortality are age, burn size, and the presence of inhalation injury. Our objective was to describe temporal trends in patient and burn characteristics, inpatient mortality, and the relationship between these characteristics and inpatient mortality over time. All patients aged 18 years or older and admitted with burn injury, including inhalation injury only, between 2004 and 2013 were included. Adjusted Cox proportional hazards regression models were used to estimate the relationship between admit year and inpatient mortality. A total of 5540 patients were admitted between 2004 and 2013. Significant differences in sex, race/ethnicity, burn mechanisms, TBSA, inhalation injury, and inpatient mortality were observed across calendar years. Patients admitted between 2011 and 2013 were more likely to be women, non-Hispanic Caucasian, with smaller burn size, and less likely to have an inhalation injury, in comparison with patients admitted from 2004 to 2010. After controlling for patient demographics, burn mechanisms, and differential lengths of stay, no calendar year trends in inpatient mortality were detected. However, a significant decrease in inpatient mortality was observed among patients with extensive burns (≥75% TBSA) in more recent calendar years. This large, tertiary care referral burn center has maintained low inpatient mortality rates among burn patients over the past 10 years. While observed decreases in mortality during this time are largely due to changes in patient and burn characteristics, survival among patients with extensive burns has improved.

Antimicrobial resistance in pathogenic gram-negative bacteria is one of the most pressing challenges in the field of infectious diseases and is one of 4 key areas of unmet medical need identified by the Antibacterial Resistance Leadership Group (ARLG). The mission of the Gram-Negative Committee is to advance our knowledge of these challenging infections and implement studies to improve patient outcomes. Studies have fallen primarily into 2 broad categories: prospective cohort studies and interventional trials. Among the observational studies, CRACKLE (Consortium on Resistance Against Carbapenems in Klebsiella pneumoniae and Other Enterobacteriaceae) has contributed seminal multicenter data describing risk factors and clinical outcomes of carbapenem-resistant Enterobacteriaceae (CRE) in sentinel US hospitals. Building on this success, CRACKLE II will expand the network to hospitals across the United States and Colombia. Similar protocols have been proposed to include Acinetobacter baumannii and Pseudomonas aeruginosa (SNAP and POP studies). In addition, the CREST study (Carbapenem-Resistant Enterobacteriaceae in Solid Organ Transplant Patients) has provided pivotal data on extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae and CRE carriage among solid organ transplant recipients to inform management of this vulnerable patient population. Two clinical trials to define novel ways of using an existing antibiotic, fosfomycin, to treat ESBL-producing Enterobacteriaceae (one that has completed enrollment and the other in late protocol development) will determine the clinical efficacy of fosfomycin as step-down oral therapy to treat complicated urinary tract infections. Additional clinical studies and trials using immunotherapeutic or newly approved agents are also in the planning stage, with the main goals of generating actionable data that will inform clinical decision making and facilitate development of new treatment options for highly resistant gram-negative bacterial infections., (© The Author 2017. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com.)

Background: Polymyxins including colistin are an important "last-line" treatment for infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKp). Increasing use of colistin has led to resistance to this cationic antimicrobial peptide., Methods: A cohort nested within the Consortium on Resistance against Carbapenems in Klebsiella pneumoniae (CRACKLE) was constructed of patients with infection, or colonization with CRKp isolates tested for colistin susceptibility during the study period of December, 2011 to October, 2014. Reference colistin resistance determination as performed by broth macrodilution was compared to results from clinical microbiology laboratories (Etest) and to polymyxin resistance testing. Each patient was included once, at the time of their first colistin-tested CRKp positive culture. Time to 30-day in-hospital all-cause mortality was evaluated by Kaplan-Meier curves and Cox proportional hazard modeling., Results: In 246 patients with CRKp, 13% possessed ColR CRKp. ColR was underestimated by Etest (very major error rate = 35%, major error rate = 0.4%). A variety of rep-PCR strain types were encountered in both the ColS and the ColR groups. Carbapenem resistance was mediated primarily by blaKPC-2 (46%) and blaKPC-3 (50%). ColR was associated with increased hazard for in-hospital mortality (aHR 3.48; 95% confidence interval, 1.73-6.57; P < .001). The plasmid-associated ColR genes, mcr-1 and mcr-2 were not detected in any of the ColR CRKp., Conclusions: In this cohort, 13% of patients with CRKp presented with ColR CRKp. The apparent polyclonal nature of the isolates suggests de novo emergence of ColR in this cohort as the primary factor driving ColR. Importantly, mortality was increased in patients with ColR isolates., (© The Author 2016. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail: journals.permissions@oup.com)

Ceftolozane/tazobactam and ceftazidime/avibactam are 2 novel β-lactam/β-lactamase combination antibiotics. The antimicrobial spectrum of activity of these antibiotics includes multidrug-resistant (MDR) gram-negative bacteria (GNB), including Pseudomonas aeruginosa. Ceftazidime/avibactam is also active against carbapenem-resistant Enterobacteriaceae that produce Klebsiella pneumoniae carbapenemases. However, avibactam does not inactivate metallo-β-lactamases such as New Delhi metallo-β-lactamases. Both ceftolozane/tazobactam and ceftazidime/avibactam are only available as intravenous formulations and are dosed 3 times daily in patients with normal renal function. Clinical trials showed noninferiority to comparators of both agents when used in the treatment of complicated urinary tract infections and complicated intra-abdominal infections (when used with metronidazole). Results from pneumonia studies have not yet been reported. In summary, ceftolozane/tazobactam and ceftazidime/avibactam are 2 new second-generation cephalosporin/β-lactamase inhibitor combinations. After appropriate trials are conducted, they may prove useful in the treatment of MDR GNB infections. Antimicrobial stewardship will be essential to preserve the activity of these agents., (© The Author 2016. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail journals.permissions@oup.com.)

Klebsiella pneumoniae has become one of the most dangerous causative agents of hospital infections due to the acquisition of resistance to carbapenems, one of the last resort families of antibiotics. Resistance is usually mediated by carbapenemases coded for by different classes of genes. A prolonged outbreak of carbapenem-resistant K. pneumoniae infections has been recently described in northeastern Ohio. Most strains isolated from patients during this outbreak belong to MLST sequence type 258 (ST258). To understand more about this outbreak two isolates (strains 140 and 677), one of them responsible for a fatal infection, were selected for genome comparison analyses. Whole genome map and sequence comparisons demonstrated that both strains are highly related showing 99% average nucleotide identity. However, the genomes differ at the so-called high heterogeneity zone (HHZ) and other minor regions. This study identifies the potential value of the HHZ as a potential marker for K. pneumoniae clinical and epidemiological studies., (© The Author 2016. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.)

Objectives: Carbapenem-resistant Klebsiella pneumoniae (CRKP) is an important healthcare-associated pathogen. We evaluated the impact of CRKP strain type and treatment on outcomes of patients with CRKP bacteriuria., Patients and Methods: Physician-diagnosed CRKP urinary tract infection (UTI)-defined as those patients who received directed treatment for CRKP bacteriuria-was studied in the multicentre, prospective Consortium on Resistance against Carbapenems in Klebsiella pneumoniae (CRaCKle) cohort. Strain typing by repetitive extragenic palindromic PCR (rep-PCR) was performed. Outcomes were classified as failure, indeterminate or success. Univariate and multivariate ordinal analyses to evaluate the associations between outcome, treatment and strain type were followed by binomial analyses., Results: One-hundred-and-fifty-seven patients with physician-diagnosed CRKP UTI were included. After adjustment for CDC/National Healthcare Safety Network (NHSN)-defined UTI, critical illness and receipt of more than one active antibiotic, patients treated with aminoglycosides were less likely to fail therapy [adjusted OR (aOR) for failure 0.34, 95% CI 0.15-0.73, P=0.0049]. In contrast, patients treated with tigecycline were more likely to fail therapy (aOR for failure 2.29, 95% CI 1.03-5.13, P=0.0425). Strain type data were analysed for 55 patients. The predominant clades were ST258A (n=18, 33%) and ST258B (n=26, 47%). After adjustment for CDC/NHSN-defined UTI and use of tigecycline and aminoglycosides, infection with strain type ST258A was associated with clinical outcome in ordinal analysis (P=0.0343). In multivariate binomial models, strain type ST258A was associated with clinical failure (aOR for failure 5.82, 95% CI 1.47-28.50, P=0.0113)., Conclusions: In this nested cohort study of physician-diagnosed CRKP UTI, both choice of treatment and CRKP strain type appeared to impact on clinical outcomes., (© The Author 2014. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

Macrophage migration inhibitory factor (MIF) is an immune mediator encoded in a functionally polymorphic locus. We found the genotype conferring low expression of MIF to be enriched in a cohort of 180 patients with gram-negative bacteremia, compared with 229 healthy controls (odds ratio [OR], 2.4; P = .04), an association that was more pronounced in older adults (OR, 4.6; P = .01). Among older subjects, those with low expression of MIF demonstrated 20% reduced MIF production from lipopolysaccharide-stimulated peripheral blood monocytes and 30% lower monocyte surface Toll-like receptor 4, compared with those with high expression. Our work suggests that older adults with low expression of MIF may be predisposed to hyporesponsiveness to lipopolysaccharide and gram-negative bacterial infection.

Objective: Many patients with schizophrenia are not treated in line with evidence-based guidelines. This study examines the large-scale implementation of the National Multidisciplinary Guideline for schizophrenia in the Netherlands., Design: /st> Observational, prospective study, with repeated measurement., Setting: Thirty mental healthcare teams in different regions of the Netherlands., Participants: Three hundred and fifty-nine clinicians with different professional backgrounds and 1489 patients suffering from schizophrenia., Intervention(s): Six evidence-based interventions for schizophrenia were implemented, in the context of a quality improvement collaborative: assertive community treatment (ACT) or its adapted version functional assertive community treatment (FACT), cognitive behavioural therapy, psycho-education, family interventions, individual placement support and pharmacotherapy., Main Outcome Measure(s): Professional performance, social functioning and relapse rates., Results: Improved professional performance, in line with guidelines. Availability of (F)ACT improved from 23 to 60%. Individual Placement Support improved from 20 to 53%. Complete care plans were composed for 38% of the patients and routine outcome monitoring was introduced in most teams. Social functioning improved slightly (HoNOS mean: from 6.2 to 5.6). Relapse rates did not improve during the course of the study., Conclusions: An intensive implementation programme can result in an improved delivery of evidence-based care, increased continuity of care and slightly improved outcomes for individuals with schizophrenia. More rigorous research designs have to confirm these findings.

Infections remain a major threat to the well-being of our growing aged population. The correct and timely diagnosis of infections in older adults is increasingly important in the current age of antimicrobial resistance. Urinary tract infection, pneumonia, and bacteremia present particular challenges. In older patients with bacteremia, blood cultures have comparable yield as compared with younger patients. However, the routine triggers for ordering blood cultures may not be appropriate in older adults. In addition, resistance patterns of isolated pathogens may change with age. The main difficulties in diagnosing urinary tract infections in older adults are caused by an increased prevalence of asymptomatic bacteriuria and frequent use of urinary catheters. However, a combined noninvasive approach that includes history, physical examination, urinary dipstick testing, urine cultures, and simple blood tests can provide direction. In addition, specific guidelines for specific populations are available. In older patients suspected of bacterial pneumonia, bedside pulse oximetry and urinary antigen testing for Streptococcus pneumoniae and Legionella pneumophila provide direction for the clinician. Although infected older adults pose specific and unique diagnostic challenges, a thorough history and physical examination combined with minimally invasive testing will lead to the correct diagnosis in most older adults with infectious diseases, limiting the need for empiric antibiotics in this age group.