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Community-Associated MRSA: The March Continues

New reports indicate that the incidence of these infections and of associated disease is on the increase.

Methicillin-resistant Staphylococcus aureus (MRSA) infections are increasingly common in patients who have neither contact with hospital settings nor other established risk factors for the condition (see JW Pediatr Adolesc Med Feb 2 2004). Two recent reports on community-acquired MRSA provide insight from community-wide and individual-case perspectives.

Fridkin and colleagues used population-based surveillance data from Baltimore and Atlanta and laboratory surveillance data from 12 Minnesota hospitals to identify cases of MRSA infections. Infections were classified as community-acquired if the patients had no apparent risk factors (1647 community-acquired cases; about 10%–20% of MSRA isolates). Of these, 77% were skin and soft-tissue infections; only 6% were invasive. The incidence of community-associated MRSA infection varied by site (25.7 cases/100,000 in Atlanta; 18/100,000 in Baltimore). Risk was significantly higher in children under 2 years of age than in older patients (relative risk, 1.51) and in blacks compared with whites in Atlanta (RR, 2.7). Twenty-three percent of patients were hospitalized specifically for MRSA infection. Isolates were generally sensitive to vancomycin (100%), rifampin (98%), trimethoprim-sulfamethoxazole (97%), linezolid (96%), and clindamycin (87%). Although patterns of antimicrobial resistance varied significantly between sites, 73% of the MRSA strains were resistant to the prescribed antibiotic.

Until recently, S. aureus has rarely been associated with necrotizing fasciitis (NF). Miller and colleagues identified 14 patients at one hospital in Los Angeles with MRSA-associated NF (among 843 patients whose wound cultures grew MRSA over the course of 1 year). Patient ages ranged from 26 to 78 years; 71% had chronic disease or well-known risk factors, but nearly 30% had no identifiable risk factors. None died, but all received combined medical and surgical therapy.

Comment: What do these studies tell us? As the author of an accompanying editorial notes, the important question is what proportion of community-acquired staphylococcus disease is methicillin-resistant. (His estimate was about 5% in the Atlanta area.) For noninvasive skin and soft-tissue infections, therapy with a traditional antibiotic is reasonable, but the condition must be monitored carefully. For children with serious or life-threatening disease, vancomycin may be required initially. Antibiotic therapy can then be tailored when sensitivities are available.

— Howard Bauchner, MD

Published in Journal Watch Pediatrics and Adolescent Medicine April 25, 2005

Citation(s):

Fridkin SK et al. Methicillin-resistant Staphylococcus aureus disease in three communities. N Engl J Med 2005 Apr 7; 352:1436-44.

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Miller LG et al. Necrotizing fasciitis caused by community-associated methicillin-resistant Staphylococcus aureus in Los Angeles. N Engl J Med 2005 Apr 7; 352:1445-53.

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Chambers HF. Community-associated MRSA — Resistance and virulence converge. N Engl J Med 2005 Apr 7; 352:1485-7.

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