MRSA Continues to Invade Our Communities

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections, mostly of the skin and soft tissues, are rapidly increasing throughout the U.S. and elsewhere. In a study in a poor urban population that receives care through the Cook County Hospital and its affiliated clinics in Chicago, for example, investigators found a nearly sevenfold rise in the incidence of CA-MRSA infections from 2000 to 2005, while the frequency of methicillin-susceptible staphylococcal (MSSA) infections remained stable.1 In this population, factors associated with increased risk for CA-MRSA infections included African American ethnicity, recent incarceration, and residence in certain public housing complexes. In previous studies, parenteral drug abusers, men who have sex with men, children, military personnel, Native Americans, Pacific Islanders, prisoners, and athletes (especially those engaging in contact sports) were also identified as groups with increased risk for CA-MRSA infections. In several areas, infections with CA-MRSA are so common, however, that epidemiologic risk factors are not very reliable predictors of which skin and soft-tissue infections are likely to be caused by these organisms.

Nor do clinical features reliably distinguish CA-MRSA from MSSA infections. Cutaneous abscesses, often with necrosis and surrounding cellulitis, appear most often with CA-MRSA infections. A clinical review of available data on these infections2 demonstrates that the absence of randomized, controlled trials keeps us ignorant about virtually every important aspect of their management. Only one nearly unanimous verdict emerges from the review: Incision and drainage are critical in the therapy of purulent lesions. The role, if any, of antimicrobial agents in decreasing the duration of infection, complication rates, or recurrence rates is unknown. Although CA-MRSA is usually susceptible to trimethoprim-sulfamethoxazole, tetracyclines, and clindamycin, most of the studies failed to demonstrate a convincing benefit from systemic antimicrobial therapy. The recommendation, repeated in this review, to use such therapy in patients with abscesses >5 cm in diameter comes from a single study in children and was not confirmed in another retrospective report. If systemic antimicrobial therapy proves beneficial, an important issue involves the use of clindamycin: Some strains susceptible to this antibiotic but not to erythromycin can potentially develop clindamycin resistance during therapy. How frequently this occurs — and whether there are any attendant therapeutic implications — remains uncertain.