Researchers Examine Epidemiology of MRSA in SSTIs in Suburban Primary Care


Reports from urban medical centers suggest that methicillin-resistant Staphylococcus aureus (MRSA) has become the most common cause of skin and soft-tissue infections (SSTIs). Risk factors for MRSA have been identified but have not been clinically useful. From May 2006 to April 2007, Charles Weiss and colleagues at Palo Alto Medical Foundation in Palo Alto, Calif. performed an observational study of 529 SSTIs among ambulatory patients in the urgent care departments of a large suburban primary-care practice. SSTIs were included if they produced pus or fluid. Their research was published in BMC Research Notes. 

The proportion of MRSA was determined overall (defined as prevalence) and by SSTI diagnosis. Potential risk factors for MRSA were examined with multivariate analysis, and descriptive statistics were generated for follow-up and abscess management. The prevalence of MRSA was 22 percent and did not rise during the study. MRSA was isolated from 36 percent of abscesses, 15 percent of cellulitis, and 14 percent of other SSTIs.

Independent risk factors for MRSA included a prior history of MRSA (adjusted odds ratio [aOR], 41.05; 95% confidence interval [CI], 11.4-147.3), a close contact with prior MRSA (aOR, 12.83; 95% CI, 4.2-39.2), erythema > 10 cm (aOR, 2.59; 95% CI, 1.5-4.4), and abscess diagnosis (aOR, 3.19; 95% CI, 2.1-5.0). Prior MRSA had a positive predictive value of 88 percent for current MRSA. When both abscess diagnosis and erythema > 10 cm were present, the proportion of MRSA was 59 percent. The vast majority of SSTIs (96 percent) resolved or improved within one week. Most abscesses, even small ones, were treated with antibiotics. Resource utilization was highest in those abscesses with erythema > 10 cm.

The researchers conclude that the prevalence of MRSA is relatively low among SSTIs in suburban primary care. However, MRSA is common in the subgroup of abscesses with large erythema. While the effectiveness of adjunctive antibiotic therapy for large abscesses is unknown, drugs chosen for these infections should be active against MRSA. Most non-abscess SSTIs do not require treatment with a MRSA-active drug, and antibiotics are probably overused for small abscesses. They say that a history of prior MRSA should be recorded in a patient's health record.

Reference: Weiss C, Kaminsky P, Boggs J and Ley C. Skin and soft-tissue infections in suburban primary care: epidemiology of methicillin-resistant Staphylococcus aureus and observations on abscess management. BMC Research Notes 2011, 4:33.

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