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MRSA Attacking Outside the Hospital

Strains of methicillin-resistant Staphylococcus aureus are increasingly common in the community, although they differ from the usual, nosocomial MRSA isolates in their molecular biology, antimicrobial susceptibility, and activity. Several reports document the spread and clinical presentations of these infections.

Fridkin and colleagues studied MRSA isolates from patients in Baltimore, Atlanta, and several Minnesota communities. Infections were classified as community acquired if the patients had no apparent risk factors for the infection (10%-20% of infections); nearly 80% were skin and soft-tissue infections, primarily abscesses. Almost 75% of patients received antibiotics to which the isolates were resistant, but the course of disease did not differ between these patients and patients who received antimicrobials to which the organism was susceptible.

Until recently, S. aureus has rarely been associated with necrotizing fasciitis (NF). Miller and colleagues identified 14 patients who presented to a Los Angeles hospital from the community with MRSA and NF. Most had predisposing conditions, such as injection drug use, diabetes, or AIDS, but nearly 30% had no identifiable risk factors. Onset in these patients was typically subacute (average duration of symptoms before admission, 6 days), and the infections most commonly occurred on the extremities or buttocks. All patients survived, but most required extensive surgery and lengthy hospitalization. The authors conclude that MRSA-associated NF is an emerging clinical entity.

Ruiz and colleagues describe four cases of community-acquired MRSA pyomyositis, rarely reported in temperate climates, seen at one Washington, D.C., hospital within 6 months. All patients had infections in one thigh, and two had preceding boils that had been drained. Exposure to these organisms represents some risk to healthcare personnel. Nordmann and Naas describe a skin infection that developed in a microbiologist 7 days after working with the identical strain in the laboratory.

Comment: These community-acquired MRSA strains carry Panton-Valentine leukocidin, a membrane toxin associated with a severe inflammatory response and rarely found in nosocomial isolates. Dermatologists should realize that an increasing proportion of cutaneous staphylococcal infections in the community is due to these strains, which typically cause abscesses, often accompanied by tissue necrosis. Incision and drainage remain the most important treatment. The role of antibiotic therapy is less clear, except in severe infections like necrotizing fasciitis.

— Jan V. Hirschmann, MD

Published in Journal Watch Dermatology April 26, 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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Ruiz ME et al. Pyomyositis caused by methicillin-resistant Staphylococcus aureus. N Engl J Med 2005 Apr 7; 352:1488-9.

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Nordmann P and Naas T. Transmission of methicillin-resistant Staphylococcus aureus to a microbiologist. N Engl J Med 2005 Apr 7; 352:1489-90.

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