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BACKGROUND: Nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) plays a key role in the epidemiology and pathogenesis of disease. The purpose of this study was to determine the characteristics and dynamics of nasal strains of MRSA, as well as their relation to community-associated disease activity. METHODS: This study is a cross-sectional survey and molecular epidemiologic analysis of nasal colonization by S. aureus in homeless and runaway youths, an underserved population at high risk for staphylococcal disease. RESULTS: Of the 308 study participants, 27.6% carried S. aureus, and 6.2% carried MRSA. Subgroups of individuals with increased MRSA carriage rates were also at highest risk for community-associated MRSA infection; these subgroups included individuals with either HIV infection or AIDS, injection drug users, patients with abscesses, and those recently hospitalized. Multilocus sequence typing and pulsed-field gel electrophoresis identified 2 genotypes--ST59:P (USA1000) and ST8:S (USA300)--that accounted for 84.2% (16/19) of the MRSA isolates carried. The genotypes were distinct from nosocomial genotypes endemic in the hospital, although they originated from individuals with prior exposure to health care. CONCLUSIONS: Comparison of MRSA strains from asymptomatic carriers versus concurrently collected community-associated clinical strains from patients treated at local health-care facilities allowed for the identification of 3 population dynamics of nasal strains of MRSA: (1) endemic clones--for example, ST8:C and ST59:P--sustained asymptomatic carriage and infection over prolonged periods; (2) an epidemic clone, ST8:S, demonstrated enhanced capacity for rapid transmission and widespread infections; and (3) an outbreak clone, ST30:Z (USA1100), was highly infectious but exhibited poor asymptomatic transmission. Copyright © 2005 Infectious Diseases Society of America [ABSTRACT FROM AUTHOR]

Much of the literature on pulmonary embolism that is commonly referenced by emergency physicians begins with statistics concerning how often the diagnosis is missed and the lethality of pulmonary embolism if undiagnosed and untreated. It is likely that many emergency physicians continue to pursue an aggressive diagnostic strategy even in low-risk patients because of concerns about the potential for poor patient outcome and the medicolegal consequences of a missed diagnosis. The believed and often-quoted mortality and recurrence rates for untreated or missed pulmonary embolism are 26% to 30%. However, these figures originate from investigations that have little relevance to modern emergency medicine, which include studies dating to the 1940s, many of which have significant methodologic pitfalls. These data are also based primarily on either inpatient or autopsy populations, neither of which is representative of patients treated in the emergency department (ED). Analysis of untreated or missed pulmonary embolism in ambulatory patients reveals mortality and recurrence rates of less than 5%. This article discusses the background of commonly quoted pulmonary embolism statistics and highlights the need for future investigations enrolling ED patients that focus on disease outcome in this population. [ABSTRACT FROM AUTHOR]

Multidrug-resistant Escherichia coli strains belonging to a single lineage frequently account for a large proportion of extraintestinal E. coli infections in many parts of the world. However, limited information exists on the community prevalence and clonal composition of drug-susceptible E. coli strains. Between July 2007 and September 2010, we analyzed all consecutively collected Gram-negative bacterial isolates from patients with bloodstream infection (BSI) admitted to a public hospital in San Francisco for drug susceptibility and associated drug resistance genes. The E. coli isolates were genotyped for fimH single nucleotide polymorphisms (SNPs) and multilocus sequence types (MLSTs). Among 539 isolates, E. coli accounted for 249 (46%); 74 (30%) of them were susceptible to all tested drugs, and 129 (52%) were multidrug resistant (MDR). Only five MLST genotypes accounted for two-thirds of the E. coli isolates; the most common were ST131 (23%) and ST95 (18%). Forty-seven (92%) of 51 ST131 isolates, as opposed to only 8 (20%) of 40 ST95 isolates, were MDR (P < 0.0001). The Simpson's diversity index for drug-susceptible ST genotypes was 87%, while the index for MDR ST genotypes was 81%. ST95 strains were comprised of four fimH types, and one of these (f-6) accounted for 67% of the 21 susceptible isolates (P < 0.003). A large proportion (>70%) of both MDR and susceptible E. coli BSI isolates represented community-onset infections. These observations show that factors other than the selective pressures of antimicrobial agents used in hospitals contribute to community-onset extraintestinal infections caused by clonal groups of E. coli regardless of their drug resistance.

Rapid detection of nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) followed by appropriate infection control procedures reduces MRSA infection and transmission. We compared the performance and workflow of two Food and Drug Administration-approved nucleic acid amplification assays, the LightCycler MRSA Advanced Test and the Xpert MRSA test, with those of directly plated culture (MRSASelect) using 1202 nasal swabs collected at three U.S. sites. The sensitivity of the LightCycler test (95.2%; 95% CI, 89.1% to 98.4%) and Xpert assay (99%; 95% CI, 94.8% to 100%) did not differ compared with that of culture; the specificity of the two assays was identical (95.5%; 95% CI, 94.1% to 96.7%) compared with culture. However, sequencing performed on 71 samples with discordant results among the three methods confirmed the presence of MRSA in 40% of samples that were positive by both molecular methods but negative by culture. Workflow analysis from all sites including batch runs revealed average hands-on sample preparation times of 1.40, 2.35, and 1.44 minutes per sample for the LightCycler, Xpert, and MRSASelect methods, respectively. Discrete event simulation analysis of workflow efficiencies revealed that the LightCycler test used less hands-on time for the assay when greater than eight batched samples were run. The high sensitivity and specificity, low hands-on time, and efficiency gains using batching capabilities make the LightCycler test suitable for rapid batch screening of MRSA colonization., (Copyright © 2012 American Society for Investigative Pathology and the Association for Molecular Pathology. Published by Elsevier Inc. All rights reserved.)

Background: The methicillin-resistant Staphylococcus aureus clone USA300 contains a novel mobile genetic element, arginine catabolic mobile element (ACME), that contributes to its enhanced capacity to grow and survive within the host. Although ACME appears to have been transferred into USA300 from S. epidermidis, the genetic diversity of ACME in the latter species remains poorly characterized., Methodology/principal Findings: To assess the prevalence and genetic diversity of ACME, 127 geographically diverse S. epidermidis isolates representing 86 different multilocus sequence types (STs) were characterized. ACME was found in 51% (65/127) of S. epidermidis isolates. The vast majority (57/65) of ACME-containing isolates belonged to the predominant S. epidermidis clonal complex CC2. ACME was often found in association with different allotypes of staphylococcal chromosome cassette mec (SCCmec) which also encodes the recombinase function that facilities mobilization ACME from the S. epidermidis chromosome. Restriction fragment length polymorphism, PCR scanning and DNA sequencing allowed for identification of 39 distinct ACME genetic variants that differ from one another in gene content, thereby revealing a hitherto uncharacterized genetic diversity within ACME. All but one ACME variants were represented by a single S. epidermidis isolate; the singular variant, termed ACME-I.02, was found in 27 isolates, all of which belonged to the CC2 lineage. An evolutionary model constructed based on the eBURST algorithm revealed that ACME-I.02 was acquired at least on 15 different occasions by strains belonging to the CC2 lineage., Conclusions/significance: ACME-I.02 in diverse S. epidermidis isolates were nearly identical in sequence to the prototypical ACME found in USA300 MRSA clone, providing further evidence for the interspecies transfer of ACME from S. epidermidis into USA300.

We performed a longitudinal analysis of 661 methicillin-resistant Staphylococcus aureus (MRSA) isolates obtained from patients in a long-term care facility. USA300 clone increased from 11.3% of all MRSA isolates in 2002 to 64.0% in 2006 (p<0.0001) and was mostly recovered from skin or skin structures (64.3% vs. 27.0% for non-USA300 MRSA; p<0.0001).

Background: Persistent MRSA bacteremia (PB) represents an important subset of Staphylococcus aureus infections and correlates with poor clinical outcomes., Methods: We profiled relevant in vitro phenotypic and genotypic characteristics of MRSA isolates from 39 persons with bacteremia (21 had PB and 18 had resolving bacteremia [RB]). We also compared the intrinsic virulence and responsiveness to vancomycin of selected PB and RB strains in an experimental endocarditis model (IE)., Results: PB and RB isolates differed significantly with regard to several in vitro characteristics that are believed to impact endovascular infections. PB isolates exhibited significantly more resistance to the cationic defensin hNP-1, enhanced membrane fluidity, and substantially greater adhesion to fibronectin, fibrinogen, and endothelial cells. Genotypically, PB isolates had higher frequency of SCCmec II, CC30, and spa 16; and higher rates of agr type III, cap8, tst-1, and cna carriage. Finally, a prototypic PB strain was more resistant to vancomycin treatment in the infective endocarditis model than a RB comparator strain, despite equivalent virulence profiles., Conclusions: Our findings indicate that PB isolates may have specific virulence signatures that distinguish them from RB isolates. These data suggest that methods might be developed to identify patients at higher risk for PB in real-time, thereby optimizing the effectiveness of anti-MRSA therapeutic strategies.

We performed a longitudinal analysis of 502 unique methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates originating from San Francisco jail inmates between 2000 and 2007. Strain USA300, first encountered in 2001, accounted for 82.1% (412/502) of MRSA infections. Non-USA300 MRSA strains were rarely found after 2005 (one isolate in 2006, three in 2007).

Background: Methicillin-resistant Staphylococcus aureus (MRSA) infections have become a major public health problem in both the community and hospitals. Few studies have characterized the incidence and clonal composition of disease-causing strains in an entire population. Our objective was to perform a population-based survey of the clinical and molecular epidemiology of MRSA disease in San Francisco, California., Methods: We prospectively collected 3985 MRSA isolates and associated clinical and demographic information over a 12-month period (2004-2005) at 9 San Francisco-area medical centers. A random sample of 801 isolates was selected for molecular analysis., Results: The annual incidence of community-onset MRSA disease among San Francisco residents was 316 cases per 100,000 population, compared with 31 cases per 100,000 population for hospital-onset disease. Persons who were aged 35-44 years, were men, and were black had the highest incidence of community-onset disease. The USA300 MRSA clone accounted for 234 cases of community-onset disease and 15 cases of hospital-onset disease per 100,000 population, constituting an estimated 78.5% and 43.4% of all cases of MRSA disease, respectively. Patients with community-onset USA300 MRSA versus non-USA300 MRSA disease were more likely to be male, be of younger age, and have skin and soft-tissue infections. USA300 strains were generally more susceptible to multiple antibiotics, although decreased susceptibility to tetracycline was observed in both community-onset (P = .008) and hospital-onset (P = .03) USA300 compared to non-USA300 strains., Conclusions: The annual incidence of community-onset MRSA disease in San Francisco is substantial, surpassing that of hospital-onset disease. USA300 is the predominant clone in both the community and hospitals. The dissemination of USA300 from the community into the hospital setting has blurred its distinction as a community-associated pathogen.

The epidemic character of community-associated methicillin-resistant Staphylococcus aureus, especially the geographically widespread clone USA300, is poorly understood. USA300 isolates carry a type IV staphylococcal chromosomal cassette mec (SCCmec) element conferring beta-lactam antibiotic class resistance and a putative pathogenicity island, arginine catabolic mobile element (ACME). Physical linkage between SCCmec and ACME suggests that selection for antibiotic resistance and for pathogenicity may be interconnected. We constructed isogenic mutants containing deletions of SCCmec and ACME in a USA300 clinical isolate to determine the role played by these elements in a rabbit model of bacteremia. We found that deletion of type IV SCCmec did not affect competitive fitness, whereas deletion of ACME significantly attenuated the pathogenicity or fitness of USA300. These data are consistent with a model in which ACME enhances growth and survival of USA300, allowing for genetic "hitchhiking" of SCCmec. SCCmec in turn protects against exposure to beta-lactams.

Background: Infection with multidrug-resistant, community-associated, methicillin-resistant Staphylococcus aureus (MRSA) has been reported but seems to be isolated., Objective: To determine the incidence of a multidrug-resistant MRSA clone (USA300) in San Francisco, and to determine risk factors for the infection., Design: Population-based survey and cross-sectional study using chart review., Setting: 9 hospitals in San Francisco (population-based survey) and 2 outpatient clinics in San Francisco and Boston (cross-sectional study)., Patients: Persons with culture-proven MRSA infections in 2004 to 2006., Measurements: Annual incidence, spatial clustering, and risk factors for multidrug-resistant USA300 infection. Pulsed-field gel electrophoresis, polymerase chain reaction assays, and DNA sequencing were used to characterize MRSA isolates., Results: The overall incidence of multidrug-resistant USA300 infection in San Francisco was 26 cases per 100,000 persons (95% CI, 16 to 36 cases per 100,000 persons); the incidence was higher in 8 contiguous ZIP codes with a higher proportion of male same-sex couples. Male-male sex was a risk factor for multidrug-resistant USA300 infection (relative risk, 13.2 [CI, 1.7 to 101.6]; P < 0.001) independent of past MRSA infection (relative risk, 2.1 [CI, 1.2 to 3.7]; P = 0.007) or clindamycin use (relative risk, 2.1 [1.2 to 3.6]; P = 0.007). The risk seemed to be independent of HIV infection. In San Francisco, multidrug-resistant USA300 manifested most often as infection of the buttocks, genitals, or perineum. In Boston, the infection was recovered exclusively from men who had sex with men., Limitations: The study was retrospective, and sexual risk behavior was not assessed., Conclusion: Infection with multidrug-resistant USA300 MRSA is common among men who have sex with men, and multidrug-resistant MRSA infection might be sexually transmitted in this population. Further research is needed to determine whether existing efforts to control epidemics of other sexually transmitted infections can control spread of community-associated, multidrug-resistant MRSA.

Empirical use of beta-lactam antibiotics, the preferred agents for treating uncomplicated skin and soft tissue infections, may no longer be appropriate for these infections because of the increasing prevalence of community strains of methicillin-resistant Staphylococcus aureus (MRSA). Retrospective studies, however, suggest that outcomes are good even when beta-lactams are used. We conducted a randomized, double-blind trial of 166 outpatient subjects comparing placebo to cephalexin at 500 mg orally four times for 7 days after incision and drainage of skin and soft tissue abscesses. The primary outcome was clinical cure or failure 7 days after incision and drainage. S. aureus was isolated from 70.4% of abscess cultures. Of the isolates tested 87.8% were MRSA, 93% of which were positive for Panton-Valentine leucocidin genes. Clinical cure rates were 90.5% (95% confidence interval, 0.82 to 0.96) in the 84 placebo recipients and 84.1% (95% confidence interval, 0.74 to 0.91) in the 82 cephalexin recipients (difference in the two proportions, 0.0006; 95% confidence interval, -0.0461 to 0.0472; P = 0.25). The 90.5% cure rate observed in the placebo arm and 84.1% cure rate observed in the cephalexin arm provide strong evidence that antibiotics may be unnecessary after surgical drainage of uncomplicated skin and soft tissue abscesses caused by community strains of MRSA.

Community-onset methicillin-resistant Staphylococcus aureus (CO-MRSA) skin and soft tissue infections (SSTI) are associated with SCCmec IV and Panton-Valentine leukocidin (PVL) genes. CO-MRSA epidemiologic studies suggest that genotypic variation exists within one geographic region. We compared MRSA genotypes and demographic and clinical characteristics of patients with CO-MRSA SSTI between two regional medical centers. We also examined factors associated with SCCmec IV and PVL carriage. A total of 279 MRSA SSTI isolates from 2000 to 2002 at San Francisco General Hospital (SFGH) and Stanford University Hospital (SUH) were genotyped by pulsed-field gel electrophoresis and PCR for SCCmec and PVL genes. Medical records were reviewed for clinical characteristics. Ninety-three percent and 69% of MRSA SSTI were caused by CO-MRSA at SFGH and SUH, respectively. Patients with CO-MRSA SSTI at SFGH were more likely to be nonwhite, younger, homeless, and have no previous exposure to health care (P < 0.01). SFGH CO-MRSA strains were more likely to carry SCCmec type IV and PVL genes (90% and 55%, respectively) than SUH strains (29% and 16%, respectively). In multivariate analyses, nonwhite ethnicity was associated with both SCCmec type IV and PVL carriage (odds ratio [OR] of 2.65 and 95% confidence interval [CI] of 1.19 to 5.95 and OR of 1.94 and 95% CI of 1.03 to 3.65, respectively). ST8:USA300:IV became the dominant clone at SFGH, but not at SUH, by 2002. Despite geographic proximity, CO-MRSA SSTI exhibited differing SCCmec types, PVL carriage, and clonal dynamics. CO-MRSA SSTI at SUH were more likely to represent feral isolates of nosocomial origin. Clinicians should assess for nosocomial and community risk factors, realizing that different populations with CO-MRSA SSTI may require separate antimicrobial strategies.

We describe a case of treatment failure caused by a strain of USA300 community-associated methicillin-resistant Staphylococcus aureus (MRSA) with intermediate susceptibility to vancomycin and reduced susceptibility to daptomycin. The strain was isolated from the bone of a 56-year-old man with lumbar osteomyelitis after a 6-week treatment course of vancomycin for catheter-associated septic thrombophlebitis.

Background: Community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) infection has become common worldwide. Some researchers have argued that empirical therapy for MRSA should be given only to patients with suspected CA S. aureus infections who have risk factors for acquisition of MRSA. However, there are no prospective data examining this approach., Methods: We prospectively enrolled consecutive patients who were hospitalized with S. aureus infection, administered a detailed questionnaire, and collected clinical and microbiological information., Results: Of the 280 consenting patients, 180 were adults with CA S. aureus infection. Among these subjects, 108 (60%) had MRSA infection, and 78 (40%) had methicillin-susceptible S. aureus (MSSA) infection. MRSA infection was associated with younger age (P<.0001); skin/soft-tissue infection (P=.015); snorting/smoking illegal drugs (P=.01); recent incarceration (P=.03); lower comorbidity index (P=.01); more frequent visits to bars, raves, and/or clubs (P=.03); and higher frequency of laundering clothes in hot water (P=.05). However, the sensitivity, specificity, and predictive values for these factors for discriminating CA-MRSA infection from CA-MSSA infection were relatively poor. Post-hoc modeling revealed that, even in a 10% (i.e., low) MRSA prevalence population, patients lacking the 3 strongest MRSA risk factors would still have a 7% posttest probability of MRSA. Most MRSA strains belonged to the ST-8/USA300 genotype, contained SCCmec type IV, and shared virulence factors commonly found in the ST1:USA400 clone. MSSA strains were genotypically heterogeneous., Conclusions: We found that clinical and epidemiological risk factors in persons hospitalized for CA S. aureus infection cannot reliably distinguish between MRSA and MSSA. Our findings have important implications for the choice of empirical antibiotic therapy for suspected S. aureus infections and for infection control.

Neonatal necrotizing fasciitis is rare and is predominantly associated with methicillin-susceptible Staphylococcus aureus (MSSA). Necrotizing fasciitis associated with community-associated methicillin-resistant S aureus (CA-MRSA) has only recently been reported in the literature, primarily among adults. We present a case of a previously healthy neonate with necrotizing fasciitis of the back caused by CA-MRSA, pulsed-field type USA-300. We describe a 5-day-old infant with necrotizing fasciitis of the back caused by CA-MRSA. Treatment of necrotizing fasciitis requires prompt medical evaluation, prompt surgical debridement, and appropriate antibiotic selection. The potential involvement of CA-MRSA in necrotizing fasciitis in children needs to be considered before institution of antibiotics.

Purpose: To report the microbiological, clinical, and pathological characteristics of community-associated methicillin-resistant Staphylococcus aureus (CAMRSA) infections of the eye and orbit., Design: Prospective case series., Participants: Nine patients with CAMRSA infections of the eye and orbit were identified during a 6-month period at 2 tertiary care hospitals in San Francisco., Methods: Case identification was by prospective case selection and retrospective laboratory review of 549 MRSA cultures collected in the 2 hospitals. Ophthalmic microbial isolates were analyzed by pulsed-field gel electrophoresis and compared with a control CAMRSA clone (USA300). Clinical characteristics of patients infected with CAMRSA were reviewed, and all surgical specimens underwent pathological examination., Main Outcome Measures: Pulsed-field gel electrophoresis banding patterns of MRSA isolates, antibiotic sensitivity profiles, patient demographics, systemic and ocular complications of infection, and posttreatment visual acuities., Results: Nine ophthalmic isolates were CAMRSA clone USA300. The infections included orbital cellulitis, endogenous endophthalmitis, panophthalmitis, lid abscesses, and septic venous thrombosis. Patients were treated with trimethoprim-sulfamethoxazole, rifampin, clindamycin, or vancomycin based on microbial sensitivity studies and severity of infection. Eight of the 9 patients had no history of hospitalization. Seven patients required hospitalization, 3 required surgery, and an additional 4 required invasive procedures. Eight patients had good visual outcomes, but 1 deteriorated to no light perception. Pathological analyses showed extensive necrosis in eyelid and orbital specimens, and disorganized atrophy bulbi in an enucleated eye., Conclusion: The USA300 CAMRSA clone, which carries Panton-Valentine leukocidin genes, can cause aggressive infections of the eye and orbit in hospital-naive patients. Treatment of infections often required debridement of necrotic tissues in addition to non-beta-lactam class antibiotics. In communities where CAMRSA is prevalent, ophthalmologists should obtain microbial cultures and sensitivity studies to help guide antibiotic therapy for severe ophthalmic infections.

A variety of methods for genotyping Staphylococcus aureus isolates exists: the two most widely used methods are pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Here, we describe a sequence-based genotyping method based on genes encoding S. aureus superantigen-like proteins, which belong to a family of exotoxins called staphylococcal exotoxins. The sequences of PCR-amplified internal fragments of three different set genes (set2, set5, and set7) of 61 well-characterized clinical methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) isolates and reference strains were compared. Phylogenetic analysis was performed based on single-nucleotide polymorphisms (SNP). The SNP dendrograms of the set gene sequences differentiated the 61 isolates into 22 distinct subgroups, designated exotoxin sequence types (ETST), while the standard seven-gene MLST profiles differentiated the same 61 isolates into 19 subgroups. Of the 19 different MLST subgroups, 16 corresponded to 16 distinct ETST groups. However, three MLST subgroups, ST1, ST30, and ST36, were each further separated into more than one ETST subgroup. The exotoxin-based genotyping method was able to discriminate MRSA and MSSA isolates according to their specific epidemiological characteristics. This SNP analysis of the three set genes is thus equally or more discriminatory than the seven-gene MLST method, providing a good alternative typing tool for a laboratory that has sequencing capability.

Objectives: A multidrug-resistant Escherichia coli clonal group (designated CgA) has been isolated from women with cystitis and pyelonephritis in several communities. This study was designed to determine if CgA can cause community-acquired bloodstream infections., Methods: All community-acquired bloodstream infections caused by E. coli identified at the San Francisco General Hospital between May 2001 and May 2003 were included. The diagnosis of septicemia was based on admission diagnosis. E. coli isolates were characterized by antibiotic susceptibility profile, enterobacterial repetitive intergenic consensus (ERIC2) PCR, serogrouping, and pulsed field gel electrophoresis (PFGE)., Results: A total of 127 individuals with a community-acquired bloodstream infection were identified; 48 (39%) were trimethoprim-sulfamethoxazole (SXT)-resistant. CgA, as defined by ERIC2 PCR, was responsible for 19 (15%) of these infections. Infection with a CgA isolate was associated with an admission diagnosis of cystitis or pyelonephritis (p=0.01). By PFGE, none of the CgA isolates were indistinguishable to the prototype cystitis strain; however, nine bloodstream isolates differed by fewer than six bands., Conclusions: CgA can cause community-acquired bloodstream infections, but does not appear to cause a disproportionate number of severe extraintestinal infections. This study provides evidence that UTI-causing clonal groups can cause a wide spectrum of disease and are an important clinical and public health concern.

Background: The extent to which the horizontal transfer of virulence genes has contributed to the emergence of contemporary virulent strains of methicillin-resistant Staphylococcus aureus (MRSA) in hospital and community settings is poorly understood., Methods: Epidemiologically well-characterized MRSA isolates collected over 8.5 years were genotyped and tested for the presence of 34 virulence genes., Results: Six strain types accounted for 88.2% of all MRSA infections. The evolution of contemporary hospital and community phenotypes within the CC8 and CC30 lineages--2 background genomes that produced historical pandemic MRSA clones--were associated with multiple horizontal acquisitions of virulence genes. The epidemic community phenotype of a CC8 strain, designated ST8:USA300, was linked to the acquisition of staphylococcal cassette chromosome (SCC)mec type IV, the genes for Panton-Valentine leukocidin (PVL), and the enterotoxin Q and K genes. Similarly, the epidemic community phenotype of a CC30 strain, ST30:USA1100, was linked to the acquisition of SCCmec type IV and the pvl genes. In contrast, the epidemic hospital phenotype of another CC30 strain, ST36:USA200, was associated with the acquisition of SCCmec type II, the enterotoxin A gene, and the toxic shock syndrome toxin 1 gene. The pvl genes appear not to be essential for the evolution OF other community-associated strains of mrsa, including ST8:USA500 and ST59:USA1000., Conclusions: The horizontal transfer of virulence genes, although infrequent, is epidemiologically associated with the emergence of new virulent strains of MRSA.

Severe pneumonia caused by community-associated methicillin-resistant Staphylococcus aureus (MRSA) was reported in children soon after this pathogen emerged in the United States in the 1990s. Genes for Panton Valentine leukocidin, which are present in the majority of community-associated MRSA, are thought to enhance the ability of S aureus to cause necrotizing pneumonia. Despite the rapid spread throughout the United States of community-associated MRSA and related skin and soft-tissue infections, reports of severe pneumonia in adults have been rare. We describe a case of a healthy young adult who initially was treated as an outpatient with levofloxacin for what appeared to be typical community-acquired pneumonia. He soon returned to the emergency department (ED) with rapidly fatal necrotizing pneumonia, associated with hemoptysis, leukopenia, and sepsis syndrome, that was caused by community-associated MRSA carrying genes for Panton Valentine leukocidin. This case highlights the typical features of this form of pneumonia and the need to consider MRSA when evaluating and treating severe pneumonia in the ED. It also raises the question of whether the incidence of this form of pneumonia might be increasing in communities with a high prevalence of community-associated MRSA and whether current pneumonia treatment guidelines should be modified.

To investigate the molecular evolution of methicillin-resistant Staphylococcus aureus (MRSA) in a large metropolitan area in Germany, 398 nonrepetitive MRSA isolates recovered from patients from various teaching and nonteaching hospitals in Cologne between 1984 and 1998 were characterized by pulsed-field gel electrophoresis (PFGE). On this basis, 95 representative isolates were selected and further investigated by multilocus sequence typing (MLST), spa typing, and staphylococcal cassette chromosome mec (SCCmec) typing. Overall, there were 9 MLST types and 16 spa types. The most prevalent sequence types (STs) were ST239 (38% of isolates), ST247 (29%), and ST228 (18%); the most prevalent spa types were 37 (32%) and 51 (29%). ST239 comprised five major PFGE types and various unique PFGE patterns, and ST5 comprised two PFGE types. While the same PFGE pattern was not observed among strains with different STs, spa type 37 was observed among strains representing two different STs (ST239 and ST241), and these belonged to the same clonal complex as single-locus variants. ST239 was the earliest predominant ST, with the highest prevalence from 1984 to 1988 (96%), followed by ST247 from 1989 to 1993 (83%) and ST228 from 1994 to 1998 (40%). Spa type 37 was the most prevalent from 1984 to 1988 (96%), spa type 51 was the most prevalent from 1989 to 1993 (83%), and spa types 1 and 458 were the most prevalent from 1994 to 1998 (26% and 14%, respectively). The prevalence of SCCmec type III decreased from 96% from 1984 to 1988 to 8% from 1989 to 1993, the prevalence of SCCmec type I increased from 4% from 1984 to 1988 to 97% from 1989 to 1993 and decreased to 62% from 1994 to 1998. While the genetic diversity of MRSA increased from 1984 to 1998, one prevalent ST usually accounted for most of the isolates in a given time period.

Background: The prevalence of vancomycin-resistant enterococci (VRE) is increasing, despite infection control measures. Limited data link ticarcillin-clavulanate to higher VRE prevalence., Methods: Active surveillance for VRE was conducted before and after a formulary switch from ticarcillin-clavulanate to piperacillin-tazobactam. Rectal swabs were obtained serially in 863 adult patients admitted to intensive care units (ICUs) between November 1, 2000 and September 30, 2004., Results: In the postswitch period, 38 of 497 (7.6%) patients acquired VRE versus 42 of 366 (11.5%) patients in the preswitch period. Survival analysis showed an overall hazard ratio (HR) of .68 postswitch versus preswitch ( P = .07), with the greatest change in the surgical ICU (HR = .17, P = .006). Multivariate analysis showed an overall HR = .51 ( P = .004). Hospital-wide, nonstool VRE clinical cultures fell from 39 (.58/1000 patient days) in the 10-month preswitch period to 27 (.33/1000 patient days) in the 12-month postswitch period. Infection control practices and use of other antibiotics remained stable., Conclusions: VRE acquisition appeared to decrease in association with a formulary change from ticarcillin-clavulanate to piperacillin-tazobactam.

To define methicillin-resistant Staphylococcus aureus (MRSA) reservoirs in the community and their population dynamics, we studied the molecular epidemiology of a random sample (n=490) from a collection of 2154 inpatient and outpatient MRSA isolates during a 7-year period in San Francisco. We noted a progressive replacement of type II staphylococcal chromosomal cassette (SCC)mec-bearing isolates with type IV SCCmec-bearing isolates, which coincided with >4-fold increase in methicillin resistance between 1998 and 2002. Type IV SCCmec-bearing isolates involved in the increase in methicillin resistance belonged to 4 molecular genotypes. These 4 genotypes were associated predominantly with community-onset disease, rather than hospital- or long-term-care facility-onset disease (76.9% vs. 19.4% vs. 3.7%; P=.0005), suggesting that they are not feral descendants of hospital isolates. The longitudinal results linked the dramatic increase in MRSA infections to an expanding community reservoir of MRSA genotypes with intrinsic community survival advantage.

Hypothesis: A high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in soft tissue infections presents a treatment challenge., Design: Retrospective analysis., Setting: The San Francisco General Hospital Integrated Soft Tissue Infection (ISIS) Clinic., Patients: Patients treated at the ISIS Clinic from July 1, 2000, to June 30, 2003., Main Outcome Measures: Information on patient demographics, surgical procedures, microbiologic studies, and antibiotic treatments was obtained for all patients treated in the ISIS Clinic. Microbial data and antibiotic susceptibility pattern of S aureus, treatment outcome, and antibiotic prescribed were analyzed for all evaluable patients., Results: The ISIS Clinic treated 6156 unique patients for 12,012 episodes of infection. In this cohort, 5164 (84%) were either homeless or had no health insurance. More than half of the patients (58%) were injection drug users, but most had only 1 prior visit to the clinic (62%). Patients underwent a surgical procedure 7707 times (64%). Of the 837 positive cultures obtained, S aureus was recovered 695 times (83%), and 525 (63%) of the cultures contained MRSA. Therefore, a full 76% of all S aureus isolated was MRSA. In a subset analysis of 622 cultures collected prospectively from consecutive patients, 282 (45%) grew organisms, of which 256 (91%) were S aureus. MRSA represented 59% of all S aureus isolated. Homelessness and injection drug use were risk factors for infection by S aureus and MRSA. In another subgroup of patients with soft tissue infections that required admission to the hospital, MRSA was recovered from the cultures in 149 patients. In these patients with MRSA, 44 (30%) only received a beta-lactam antibiotic, inactive against MRSA, and had full resolution of their infection., Conclusions: The prevalence of MRSA soft tissue infections in the medically underserved ISIS Clinic cohort is extremely high. The transmission of the MRSA seems to be in the community. Antibiotic therapy directed at MRSA may not be needed in a large number of patients with these soft tissue infections. Studies to identify the source and cause of this MRSA outbreak are urgently needed. Clinical trials to examine the need for antibiotic therapy in soft tissue infections should be conducted.

Infections caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) are emerging as a major public health problem. CA-MRSA has been associated previously with skin and soft-tissue infection (SSTI) and with carriage of staphylococcal cassette chromosome mec (SCCmec) type IV and the Panton-Valentine leucocidin (PVL) virulence factor. To assess the clonal distribution of PVL-carrying strains and the association with SSTI in the San Francisco Bay area, we surveyed six collections of S. aureus isolates-671 isolates in all-collected between 1997 and 2002 originating from inpatient and outpatient clinical specimens and from a community-based sampling. Isolates were genotyped by pulsed-field gel electrophoresis, multilocus restriction fragment typing, and multilocus sequence typing and assayed for the PVL virulence factor. The S. aureus populations showed a high proportion of PVL-carrying strains, with frequencies ranging up to 70% in MRSA isolated from jail inmate patients and 69% in MRSA from patients receiving surgical treatment at an outpatient clinic specializing in treating SSTIs. PVL-carrying isolates were identified in nine clonal groups, but 88.5% of the PVL-carrying MRSA isolates belonged to only two clonal groups. These two clonal groups carried the SCCmec type IV resistance determinant and were more likely than other clonal groups to be recovered from SSTI sites than from other sites (P < 0.0001). There is evidence of clonal replacement over the period from 1999 to 2002, with one of these two clonal groups being supplanted by the other.

San Francisco General Hospital (San Francisco, CA) experienced an overall increase in the recovery of methicillin-resistant Staphylococcus aureus (MRSA) isolates that were shown by pulsed-field gel electrophoresis to have a genotype (genotype A1) that was new to this institution. We performed a case-control study to identify risk factors for acquiring genotype A1 MRSA infection from 1 October 2001 to 19 July 2002. Patients with genotype A1 MRSA infection were compared with 2 control groups: MRSA-infected control patients (i.e., patients with infection due to non-genotype A1 MRSA) and non-MRSA infected control patients (i.e., hospitalized patients without MRSA infection). There were 41 case patients infected with genotype A1 MRSA, 99 control patients infected with MRSA, and 41 control patients without MRSA infection. Pneumonia, surgical wound infections, and line infections occurred more frequently among case patients. Intensive care unit exposure and invasive procedures conferred the greatest risk for genotype A1 MRSA infection in multivariate models. Case patients were not associated with increased mortality, after adjusting for age, comorbidities, and intensive care unit exposure. Genotype A1 MRSA caused a large nosocomial outbreak of infection that was associated with distinct risk factors and clinical manifestations.

The API 20 Strep system was used to speciate 46 enterococcal isolates with vancomycin MICs between 16-32 microg/mL. All were identified as Enterococcus faecium. Further testing revealed that 42/46 isolates had been identified incorrectly. Enterococci with low-level vancomycin resistance should not be speciated solely with the API 20 Strep system.