Community-Associated Methicillin-Resistant Staphylococcus aureus Skin and Soft Tissue Infections at a Public Hospital

Abstract

Background: Community-associated methicillinresistant Staphylococcus aureus (CA-MRSA) infections have emerged among patients without health careassociated risk factors. Understanding the epidemiology of CA-MRSA is critical for developing control measures.Methods: At a 464-bed public hospital in Chicago and its more than 100 associated clinics, surveillance of soft tissue, abscess fluid, joint fluid, and bone cultures for S aureus was performed. We estimated rates of infection and geographic and other risks for CA-MRSA through laboratory-based surveillance and a case-control study.Results: The incidence of CA-MRSA skin and soft tissue infections increased from 24.0 cases per 100 000 people in 2000 to 164.2 cases per 100 000 people in 2005 (relative risk, 6.84 [2005 vs 2000]). Risk factors were incarceration (odds ratio [OR], 1.92; 95% confidence in-terval [CI], 1.00-3.67), African American race/ethnicity (OR, 1.91; 95% CI, 1.28-2.87), and residence at a group of geographically proximate public housing complexes (OR, 2.50; 95% CI, 1.25-4.98); older age was inversely related (OR, 0.89; 95% CI, 0.82-0.96 [for each decade increase]). Of 73 strains tested, 79% were pulsed-field gel electrophoresis type USA300.Conclusions: Clonal CA-MRSA infection has emerged among Chicago's urban poor. It has occurred in addition to, not in place of, methicillin-susceptible S aureus infection. Epidemiological analysis suggests that control measures could focus initially on core groups that have contributed disproportionately to risk, although CA-MRSA becomes endemic as it disseminates within communities.

Long-Term Follow-Up of Methicillin-Resistant Staphylococcus aureus Molecular Epidemiology after Emergence of Clone USA300 in San Francisco Jail Populations

“…As previously reported (14,17), USA300 was primarily associated with SSSI in this study and was usually susceptible to trimethoprim-sulfamethoxazole, clindamycin, and tetracycline (3), with no significant increase in antimicrobial resistance over time, as opposed to recent reports from other settings (7,10). Large jails have been identified as likely foci for the amplification and subsequent spread of MRSA in the surrounding communities (12,13), and it was predicted that public health interventions directed at these "superspreader institutions" could have a disproportionate impact on controlling CA-MRSA epidemics (11). Our study adds another incentive for improving infection control in these institutions by showing the persistently high incidence of MRSA infections once USA300 is introduced, in the absence of dedicated intervention.…”

Prediction of Methicillin-Resistant Staphylococcus aureus Involvement in Disease Sites by Concomitant Nasal Sampling

“…This may support the idea that antimicrobial agents have only weak activity against nasal staphylococcal colonization; it may also be a product of the fact that we used an assay to detect MRSA DNA rather than viable organisms. While the anterior nares are established as the reservoir of traditional MRSA subtypes, it has been suggested that the reservoir for community-associated (CA) MRSA may lie elsewhere (8). Clindamycin susceptibility is a simple phenotypic marker for CA MRSA (17).…”

The role of virulence determinants in community-associated MRSA pathogenesis

“…Type I ACME has been postulated to contribute to growth and survival of USA300 within the host, and promote colonization of the human skin [26]. ACME is integrated downstream of type IV SCCmec (Figure 2), utilizing the same cassette chromosome recombinases A and B (ccrAB) contained with SCCmec for mobilization and transfer [15][16][17][18][19][20][21][22][23][24]34]. Type I ACME is a distinctive genetic feature of the USA300 pandemic clone [26,34,35], although ACME-like elements have been detected in sporadic MRSA [32][33][34].…”