Infection with multidrug-resistant, community-associated, methicillin-resistant Staphylococcus aureus (MRSA) has been reported but seems to be isolated.
To determine the incidence of a ...multidrug-resistant MRSA clone (USA300) in San Francisco, and to determine risk factors for the infection.
Population-based survey and cross-sectional study using chart review.
9 hospitals in San Francisco (population-based survey) and 2 outpatient clinics in San Francisco and Boston (cross-sectional study).
Persons with culture-proven MRSA infections in 2004 to 2006.
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.
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.
The study was retrospective, and sexual risk behavior was not assessed.
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.
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.
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Background. Since its emergence in 2000, epidemic spread of the methicillin-resistant Staphylococcus aureus (MRSA) clone USA300 has led to a high burden of skin and soft tissue infections (SSTIs) in ...the United States, yet its impact on MRSA bloodstream infections (BSIs) is poorly characterized. Methods. To assess clonality of the MRSA isolates causing SSTI and BSI during the epidemic period, a stratified, random sample of 1350 unique infection isolates (from a total of 7252) recovered at the Community Health Network of San Francisco from 2000 to 2008 were selected for genotyping. Risk factors and outcomes for 549 BSI cases caused by the USA300 epidemic clone and non-USA300 MRSA clones were assessed by retrospective review of patient medical records. Results. From 2000 to 2008, secular trends of USA300 SSTI and USA300 BSI were strongly correlated (Pearson r = 0.953). USA300 accounted for 55% (304/549) of BSIs as it was the predominant MRSA clone that caused community-associated (115/160), healthcare-associated community-onset (125/207), and hospital-onset (64/182) BSIs. Length of hospitalization after BSI diagnosis and mortality rates for USA300 and non-USA300 were similar. Two independent risk factors for USA300 BSI were identified: concurrent SSTI (adjusted relative risk, 1.4 95% confidence interval {CI}, 1.2–1.6) and anti-MRSA antimicrobial use in the preceding 30 days (0.7 95% CI, .6–.8). Isolates from concurrent SSTI were indistinguishable genotypically from the USA300 isolates that caused BSI. Conclusions. USA300 SSTIs serve as a source for BSI. Strategies to control the USA300 SSTI epidemic may lessen the severity of the concurrent USA300 BSI epidemic.
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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.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
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).
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DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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 conferringβ-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 toβ-lactams.
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BackgroundThe 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 MethodsEpidemiologically well-characterized MRSA isolates collected over 8.5 years were genotyped and tested for the presence of 34 virulence genes ResultsSix 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 ConclusionsThe horizontal transfer of virulence genes, although infrequent, is epidemiologically associated with the emergence of new virulent strains of MRSA
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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.
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DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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