Concurrent epidemics of skin and soft tissue infection and bloodstream infection due to community-associated methicillin-resistant Staphylococcus aureus.

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.

Emergence of multidrug-resistant, community-associated, methicillin-resistant Staphylococcus aureus clone USA300 in men who have sex with men.

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.

Complete genome sequence of USA300, an epidemic clone of community-acquired meticillin-resistant Staphylococcus aureus.

BACKGROUND: USA300, a clone of meticillin-resistant Staphylococcus aureus, is a major source of community-acquired infections in the USA, Canada, and Europe. Our aim was to sequence its genome and compare it with those of other strains of S aureus to try to identify genes responsible for its distinctive epidemiological and virulence properties. METHODS: We ascertained the genome sequence of FPR3757, a multidrug resistant USA300 strain, by random shotgun sequencing, then compared it with the sequences of ten other staphylococcal strains. FINDINGS: Compared with closely related S aureus, we noted that almost all of the unique genes in USA300 clustered in novel allotypes of mobile genetic elements. Some of the unique genes are involved in pathogenesis, including Panton-Valentine leucocidin and molecular variants of enterotoxin Q and K. The most striking feature of the USA300 genome is the horizontal acquisition of a novel mobile genetic element that encodes an arginine deiminase pathway and an oligopeptide permease system that could contribute to growth and survival of USA300. We did not detect this element, termed arginine catabolic mobile element (ACME), in other S aureus strains. We noted a high prevalence of ACME in S epidermidis, suggesting not only that ACME transfers into USA300 from S epidermidis, but also that this element confers a selective advantage to this ubiquitous commensal of the human skin. INTERPRETATION: USA300 has acquired mobile genetic elements that encode resistance and virulence determinants that could enhance fitness and pathogenicity.