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This paper is part of a clinical practice guideline update on the risk assessment, diagnostic imaging, and microbiological evaluation of complicated intra-abdominal infections in adults, children, and pregnant people, developed by the Infectious Diseases Society of America (IDSA). In this paper, the panel provides recommendations for diagnostic imaging of suspected acute appendicitis. The panel's recommendations are based on evidence derived from systematic literature reviews and adhere to a standardized methodology for rating the certainty of evidence and strength of recommendation according to the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach., Competing Interests: Potential conflicts of interest. Evaluation of relationships as potential conflicts of interest (COIs) is determined by a review process. The assessment of disclosed relationships for possible COIs 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). A. W. C. receives honoraria from UpToDate, Inc, and serves on an Agency for Healthcare Research and Quality technical expert panel for diagnosis of acute right lower quadrant abdominal pain (suspected acute appendicitis). J. R. B. serves as past president of the European Society of Clinical Microbiology and Infectious Diseases. M. S. E. receives royalties from UpToDate, Inc, as co-section editor of Pediatric Infectious Diseases. M. K. H. serves on the Society for Healthcare Epidemiology of America (SHEA) Board of Directors. 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 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.)

This paper is part of a clinical practice guideline update on the risk assessment, diagnostic imaging, and microbiological evaluation of complicated intra-abdominal infections in adults, children, and pregnant people, developed by the Infectious Diseases Society of America. In this paper, the panel provides recommendations for diagnostic imaging of suspected acute diverticulitis. The panel's recommendations are based on evidence derived from systematic literature reviews and adhere to a standardized methodology for rating the certainty of evidence and strength of recommendation according to the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach., Competing Interests: Potential conflicts of interest. Evaluation of relationships as potential conflicts of interest (COIs) is determined by a review process. The assessment of disclosed relationships for possible COIs 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). A. W. C. receives honoraria from UpToDate, Inc. J. R. B. serves as past president of the European Society of Clinical Microbiology and Infectious Diseases. M. S. E. receives royalties from UpToDate, Inc, as co-section editor of Pediatric Infectious Diseases. M. K. H. serves on the Society for Healthcare Epidemiology of America (SHEA) Board of Directors. 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 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.)

This article is part of a clinical practice guideline update on the risk assessment, diagnostic imaging, and microbiological evaluation of complicated intra-abdominal infections in adults, children, and pregnant people, developed by the Infectious Diseases Society of America. In this guideline, the panel provides recommendations for obtaining blood cultures in patients with known or suspected intra-abdominal infection. The panel's recommendations are based on evidence derived from systematic literature reviews and adhere to a standardized methodology for rating the certainty of evidence and strength of recommendation according to the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach., Competing Interests: Potential conflicts of interest. Evaluation of relationships as potential conflicts of interest (COIs) is determined by a review process. The assessment of disclosed relationships for possible COIs 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). A. W. C. receives honoraria from UpToDate, Inc; serves on an Agency for Healthcare Research and Quality technical expert panel for diagnosis of acute right lower quadrant abdominal pain (suspected acute appendicitis); and has served as an advisor for GenMark Diagnostics, Inc, on molecular diagnostics for gastrointestinal pathogens. J. R. B. serves as past president of ESCMID. M. S. E. receives royalties from UpToDate, Inc, as co–section editor of Pediatric Infectious Diseases. M. K. H. serves on the Society for Healthcare Epidemiology of America Board of Directors and has received free services from OpGen, Inc, for a research project. R. H. is an advisor for bioMérieux, Inc, and was previously an employee of Accelerate Diagnostics, Inc; has received research funding from bioMérieux, Inc; and has served as an advisor for Thermo Fisher Scientific, Inc. 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 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.)

This article is part of a clinical practice guideline update on the risk assessment, diagnostic imaging, and microbiological evaluation of complicated intraabdominal infections in adults, children, and pregnant people, developed by the Infectious Diseases Society of America. In this article, the panel provides recommendations for diagnostic imaging of suspected acute cholecystitis and acute cholangitis. The panel's recommendations are based on evidence derived from systematic literature reviews and adhere to a standardized methodology for rating the certainty of evidence and strength of recommendation according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach., Competing Interests: Potential conflicts of interest. Evaluation of relationships as potential conflicts of interest (COIs) is determined by a review process. The assessment of disclosed relationships for possible COIs 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). A. W. C. receives honoraria from UpToDate, Inc, and serves on an Agency for Healthcare Research and Quality technical expert panel for diagnosis of acute right lower quadrant abdominal pain (suspected acute appendicitis). J. R. B. serves as past president of the European Society of Clinical Microbiology and Infectious Diseases. M. S. E. receives royalties from UpToDate, Inc, as co-section editor of Pediatric Infectious Diseases. M. K. H. serves on the Society for Healthcare Epidemiology of America Board of Directors. 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 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.)

This paper is part of a clinical practice guideline update on the risk assessment, diagnostic imaging, and microbiological evaluation of complicated intra-abdominal infections in adults, children, and pregnant people, developed by the Infectious Diseases Society of America. In this paper, the panel provides a recommendation for risk stratification according to severity of illness score. The panel's recommendation is based on evidence derived from systematic literature reviews and adheres to a standardized methodology for rating the certainty of evidence and strength of recommendation according to the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) approach., Competing Interests: Potential conflicts of interest. Evaluation of relationships as potential conflicts of interest (COIs) is determined by a review process. The assessment of disclosed relationships for possible COIs 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). A. W. C. receives honoraria from UpToDate, Inc. J. R. B. serves as past president of the European Society of Clinical Microbiology and Infectious Diseases. M. S. E. receives royalties from UpToDate, Inc. as co-section editor of Pediatric Infectious Diseases. M. K. H. serves on the Society for Healthcare Epidemiology of America Board of Directors. All other authors report no relevant disclosures. 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 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.)

This article is part of a clinical practice guideline update on the risk assessment, diagnostic imaging, and microbiological evaluation of complicated intra-abdominal infections in adults, children, and pregnant people, developed by the Infectious Diseases Society of America. In this article, the panel provides recommendations for diagnostic imaging of suspected acute intra-abdominal abscess. The panel's recommendations are based on evidence derived from systematic literature reviews and adhere to a standardized methodology for rating the certainty of evidence and strength of recommendation according to the GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach., Competing Interests: Potential conflicts of interest. Evaluation of relationships as potential conflicts of interest (COIs) is determined by a review process. The assessment of disclosed relationships for possible COIs 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). A. W. C. receives honoraria from UpToDate and serves on an Agency for Healthcare Research and Quality technical expert panel for diagnosis of acute right lower quadrant abdominal pain (suspected acute appendicitis). M. S. E. receives royalties from UpToDate, as co-section editor of Pediatric Infectious Diseases. M. K. H. serves on the board of directors for the Society for Healthcare Epidemiology of America. J. R. B. serves as past president of the European Society of Clinical Microbiology and Infectious Diseases. 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 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.)

This paper is part of a clinical practice guideline update on the risk assessment, diagnostic imaging, and microbiological evaluation of complicated intra-abdominal infections in adults, children, and pregnant people, developed by the Infectious Diseases Society of America. In this paper, the panel provides recommendations for obtaining cultures of intra-abdominal fluid in patients with known or suspected intra-abdominal infection. The panel's recommendations are based on evidence derived from systematic literature reviews and adhere to a standardized methodology for rating the certainty of evidence and strength of recommendation according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach., Competing Interests: Potential conflicts of interest . Evaluation of relationships as potential conflicts of interest (COIs) is determined by a review process. The assessment of disclosed relationships for possible COIs 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). A. W. C. receives honoraria from UpToDate, Inc.; serves on an Agency for Healthcare Research and Quality technical expert panel for diagnosis of acute right lower quadrant abdominal pain (suspected acute appendicitis); and has served as an advisor for GenMark Diagnostics, Inc. on molecular diagnostics for gastrointestinal pathogens. J. R. B. serves as past president of the European Society of Clinical Microbiology and Infectious Diseases. M. S. E. receives royalties from UpToDate, Inc. as co-section editor of Pediatric Infectious Diseases. M. K. H. serves on the Society for Healthcare Epidemiology of America (SHEA) Board of Directors and has received free services from OpGen, Inc. for a research project. R. H. is an advisor for bioMerieux, Inc. and was previously an employee of Accelerate Diagnostics, Inc.; has received research funding from bioMerieux, Inc.; and served as an advisor for Thermo Fisher Scientific, Inc. All other authors reported no relevant disclosures. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest., (© 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.)

As the first part of an update to the clinical practice guideline on the diagnosis and management of complicated intra-abdominal infections in adults, children, and pregnant people, developed by the Infectious Diseases Society of America, the panel presents 21 updated recommendations. These recommendations span risk assessment, diagnostic imaging, and microbiological evaluation. The panel's recommendations are based on evidence derived from systematic literature reviews and adhere to a standardized methodology for rating the certainty of evidence and strength of recommendation according to the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) approach., Competing Interests: Potential conflicts of interest. Evaluation of relationships as potential conflicts of interest (COIs) is determined by a review process. The assessment of disclosed relationships for possible conflicts of interest 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). A. W. C. receives honoraria from UpToDate, Inc.; serves on an Agency for Healthcare Research and Quality technical expert panel for diagnosis of acute right lower quadrant abdominal pain (suspected acute appendicitis); and has served as an advisor for GenMark Diagnostics, Inc. on molecular diagnostics for gastrointestinal pathogens. J. R. B. serves as past president of the European Society of Clinical Microbiology and Infectious Diseases. M. S. E. receives royalties from UpToDate, Inc. as co-section editor of Pediatric Infectious Diseases. M. H. serves on the Society Healthcare Epidemiology of America Board of Directors and has received free services from OpGen, Inc. for a research project. R. H. is an advisor for bioMérieux, Inc. and was previously an employee of Accelerate Diagnostics, Inc.; has received research funding from bioMérieux, Inc.; and served as an advisor for Thermo Fisher Scientific, Inc. 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 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 Surgical Infection Society (SIS) published evidence-based guidelines for the management of intra-abdominal infection (IAI) in 1992, 2002, 2010, and 2017. Here, we present the most recent guideline update based on a systematic review of current literature. Methods: The writing group, including current and former members of the SIS Therapeutics and Guidelines Committee and other individuals with content or guideline expertise within the SIS, working with a professional librarian, performed a systematic review using PubMed/Medline, the Cochrane Library, Embase, and Web of Science from 2016 until February 2024. Keyword descriptors combined "surgical site infections" or "intra-abdominal infections" in adults limited to randomized controlled trials, systematic reviews, and meta-analyses. Additional relevant publications not in the initial search but identified during literature review were included. The Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) system was utilized to evaluate the evidence. The strength of each recommendation was rated strong (1) or weak (2). The quality of the evidence was rated high (A), moderate (B), or weak (C). The guideline contains new recommendations and updates to recommendations from previous IAI guideline versions. Final recommendations were developed by an iterative process. All writing group members voted to accept or reject each recommendation. Results: This updated evidence-based guideline contains recommendations from the SIS for the treatment of adult patients with IAI. Evidence-based recommendations were developed for antimicrobial agent selection, timing, route of administration, duration, and de-escalation; timing of source control; treatment of specific pathogens; treatment of specific intra-abdominal disease processes; and implementation of hospital-based antimicrobial agent stewardship programs. Summary: This document contains the most up-to-date recommendations from the SIS on the prevention and management of IAI in adult patients.

Background: Fungi frequently are isolated in intra-abdominal infections (IAI). The Study to Optimize Peritoneal Infection Therapy (STOP-IT) recently suggested short-course treatment for patients with IAI. It remains unclear whether the presence of fungi in IAI affects the optimal duration of Antimicrobial therapy. We hypothesized that a shorter treatment course in IAI with fungal organisms would be associated with a higher rate of treatment failure., Methods: Patients enrolled in the STOP-IT trial were stratified according to the presence or absence of a fungal isolate. They were analyzed as a subgroup based on original randomization to either the control group or an experimental group that received a four-day course of Antimicrobial therapy and by comparison with those without a fungal component to their infection. Descriptive comparisons were performed using a χ 2 , Fisher exact, or Kruskal-Wallis test as appropriate. The primary outcome was a composite of recurrent IAI, surgical site infection, and death., Results: A total of 411 patients in the study (79%) had available culture data, of which 58 (14%) had positive fungal cultures. The most common organisms were Candida albicans and C. glabrata. The treatment failure rate was equivalent in the experimental and control arms (29.6% vs. 22.6%; p = 0.54). Patients with fungal isolates were more likely to have malignant disease (25.9% vs. 9.6%; p = 0.0004) and coronary artery disease (22% vs. 12%; p = 0.04), but were otherwise similar to those without fungal isolates. Patients with fungal isolates had more hospital days (median 10 vs. 7; p < 0.0001) and more days to resumption of enteral intake (median 5 vs. 3; p = 0.0006), but there was no difference in the composite outcome., Conclusions: Patients with IAI involving fungal organisms randomized to a shorter course of Antimicrobial therapy had no difference in the rate of treatment failure. These results suggest that the presence of fungi in IAI may not indicate independently the need for a longer course of Antimicrobial therapy.

Desirability of outcome ranking and response adjusted for duration of antibiotic risk (DOOR/RADAR) are novel and innovative methods of evaluating data in antibiotic trials. We analyzed data from a noninferiority trial of short-course antimicrobial therapy for intra-abdominal infection (STOP-IT), and results suggest global superiority of short-duration therapy for intra-abdominal 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: Recent studies have suggested the length of treatment of intra-abdominal infections (IAIs) can be shortened without detrimental effects on patient outcomes. However, data from high-risk patient populations are lacking. We hypothesized that patients at high risk for treatment failure will benefit from a longer course of antimicrobial therapy., Methods: Patients enrolled in the Study to Optimize Peritoneal Infection Therapy (STOP-IT) trial were evaluated retrospectively to identify risk factors associated with treatment failure, which was defined as the composite outcome of recurrent IAI, surgical site infection, or death. Variables were considered risk factors if there was a positive statistical association with treatment failure. Patients were then stratified according to the presence and number of these risk factors. Univariable analyses were performed using the Kruskal-Wallis, χ 2 , and Fisher exact tests. Logistic regression controlling for risk factors and original randomization group, either a fixed four-day antimicrobial regimen (experimental) or a longer course based on clinical response (control), also was performed., Results: We identified corticosteroid use, Acute Physiology and Chronic Health Evaluation II score ≥5, hospital-acquired infection, or a colonic source of IAI as risk factors associated with treatment failure. Of the 517 patients enrolled, 263 (50.9%) had one or two risk factors and 16 (3.1%) had three or four risk factors. The rate of treatment failure rose as the number of risk factors increased. When controlling for randomization group, the presence and number of risk factors were independently associated with treatment failure, but the duration of antimicrobial therapy was not., Conclusions: We were able to identify patients at high risk for treatment failure in the STOP-IT trial. Such patients did not benefit from a longer course of antibiotic administration. Further study is needed to determine the optimum duration of antimicrobial therapy in high-risk patients.

A prospective, multicenter, randomized controlled trial found that four days of antibiotics for source-controlled complicated intra-abdominal infection resulted in similar outcomes when compared with a longer duration. We hypothesized that patients with specific risk factors for complications also had similar outcomes. Short-course patients with obesity, diabetes, or Acute Physiology and Chronic Health Evaluation II ≥15 from the STOP-IT trial were compared with longer duration patients. Outcomes included incidence of and days to infectious complications, mortality, and length of stay. Obese and diabetic patients had similar incidences of and days to surgical site infection, recurrent intra-abdominal infection, extra-abdominal infection, and Clostridium difficile infection. Short- and long-course patients had similar incidences of complications among patients with Acute Physiology and Chronic Health Evaluation II ≥15. However, there were fewer days to the diagnosis of surgical site infection (9.5 ± 3.4 vs 21.6 ± 6.2, P = 0.010) and extra-abdominal infection (12.4 ± 6.9 vs 21.8 ± 6.1, P = 0.029) in the short-course group. Mortality and length of stay was similar for all groups. A short course of antibiotics in complicated intra-abdominal infection with source control seems to have similar outcomes to a longer course in patients with diabetes, obesity, or increased severity of illness.

Background: A recent prospective, multicenter, randomized controlled trial found that 4 days of antibiotics after source control of complicated intra-abdominal infections resulted in similar outcomes when compared with longer duration. We hypothesized that the subset of patients presenting with sepsis have similar outcomes when treated with the shorter course of antibiotics., Study Design: Patients from the STOP-IT (Study to Optimize Peritoneal Infection Therapy) trial database meeting criteria for sepsis (ie, temperature <36°C or >38°C and a WBC count <4000 cells/mm(3) or >12,000 cells/mm(3)) were analyzed. Patients had been randomized to receive antibiotics until 2 days after the resolution of fever, leukocytosis, and ileus, with a maximum of 10 calendar days of therapy (n = 45), or to receive a fixed short-course of antibiotics for 4 ± 1 calendar days (n = 67). Outcomes included incidence of and time to surgical site infection, recurrent intra-abdominal infection, Clostridium difficile infection, and extra-abdominal infections, as well as hospital days and mortality., Results: One hundred and twelve of the 588 patients in the STOP-IT database met criteria for sepsis and were adherent to the protocol. With regard to short- vs long-course therapy, surgical site infection (11.9% vs 8.9%; p = 0.759), recurrent intra-abdominal infection (11.9% vs 13.3%; p = 1.00), extra-abdominal infection (11.9% vs 8.9%; p = 0.759), hospital days (7.4 ± 5.5 days vs 9.0 ± 7.5 days; p = 0.188), days to recurrent intra-abdominal infection (12.5 ± 6.6 days vs 18.0 ± 8.1 days; p = 0.185), days to extra-abdominal infection (12.6 ± 5.8 days vs 17.3 ± 3.9 days; p = 0.194), and mortality (1.5% vs 0%; p = 1.00) were similar. There were no cases of C difficile infection. Days to surgical site infection (6.9 ± 3.5 days vs 21.3 ± 6.1 days; p < 0.001) were fewer in the 4-day therapy group., Conclusions: There was no difference in outcomes between short and long-course antimicrobial therapy in patients with complicated intra-abdominal infection presenting with sepsis. Our findings suggest that the presence of systemic illness does not mandate a longer antimicrobial course if source control of complicated intra-abdominal infection is obtained., (Copyright © 2016 American College of Surgeons. Published by Elsevier Inc. All rights reserved.)

Background: The successful treatment of intraabdominal infection requires a combination of anatomical source control and antibiotics. The appropriate duration of antimicrobial therapy remains unclear., Methods: We randomly assigned 518 patients with complicated intraabdominal infection and adequate source control to receive antibiotics until 2 days after the resolution of fever, leukocytosis, and ileus, with a maximum of 10 days of therapy (control group), or to receive a fixed course of antibiotics (experimental group) for 4±1 calendar days. The primary outcome was a composite of surgical-site infection, recurrent intraabdominal infection, or death within 30 days after the index source-control procedure, according to treatment group. Secondary outcomes included the duration of therapy and rates of subsequent infections., Results: Surgical-site infection, recurrent intraabdominal infection, or death occurred in 56 of 257 patients in the experimental group (21.8%), as compared with 58 of 260 patients in the control group (22.3%) (absolute difference, -0.5 percentage point; 95% confidence interval [CI], -7.0 to 8.0; P=0.92). The median duration of antibiotic therapy was 4.0 days (interquartile range, 4.0 to 5.0) in the experimental group, as compared with 8.0 days (interquartile range, 5.0 to 10.0) in the control group (absolute difference, -4.0 days; 95% CI, -4.7 to -3.3; P<0.001). No significant between-group differences were found in the individual rates of the components of the primary outcome or in other secondary outcomes., Conclusions: In patients with intraabdominal infections who had undergone an adequate source-control procedure, the outcomes after fixed-duration antibiotic therapy (approximately 4 days) were similar to those after a longer course of antibiotics (approximately 8 days) that extended until after the resolution of physiological abnormalities. (Funded by the National Institutes of Health; STOP-IT ClinicalTrials.gov number, NCT00657566.).