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Study identifies risk factors for MRSA infections

Infection Control Monitor, May 20, 2004

A new study identified previous antibiotic use and a genetic predisposition as two major risk factors for community-acquired skin infections caused by MRSA, Hospital Business Week reports.

S. aureus is a common bacterium found on human nasal mucous membranes and skin, and strains that are resistant to methicillin can cause disease. Until recently, drug-resistant strains were thought to be acquired almost exclusively in hospital settings, but reports of MRSA acquired in the community are increasing. Such reports are most often associated with skin and soft-tissue infections such as furunculosis and cellulitis.

Risk factors for infection by community-onset MRSA have to date been poorly understood by public health officials and other scientists. To address this issue, Thomas W. Hennessy, MD, and colleagues at the CDC investigated a 1999 outbreak of furunculosis in rural southwestern Alaska. Their May 1, 2004, issue of the Journal of Infectious Diseases published their findings.

The researchers conducted a case-control study in one village located in the region of the outbreak. They identified 34 people with a laboratory-confirmed skin infection caused by community-onset MRSA, and 94 people with no history of skin infection in the previous year who were the study "controls." Hennessy and colleagues found that people with MRSA skin infections had received significantly more courses of antibiotics in the year before the outbreak than had the controls.

The research team also found that a virulence factor previously associated with skin and soft tissue infections was present in 97% of the MRSA specimens collected from a medical center in the region, compared with none of the specimens that were susceptible to methicillin. Hennessy et al concluded that the combination of methicillin resistance and the virulence factor may have provided the strain with characteristics favoring a furunculosis outbreak. The researchers developed MRSA treatment guidelines that emphasize reserving antibiotics for severe infections only.

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