Methicillin-resistant Staphylococcus aureus (MRSA): risk and outcome of colonized vs. infected patients.

A retrospective study of 204 patients culture positive for methicillin-resistant Staphylococcus aureus compared infected and colonized patients. Seventy-eight patients were colonized and never developed infection (C), 24 were colonized and subsequently infected (C----I), and 102 patients had 1 or more nosocomial infections with MRSA at time of first culture (I). The most prevalent sites of infection were wound (26.5%) and blood-stream (20.7%), whereas the respiratory tract and surgical wounds were both frequent sites of colonization. Stepwise discriminant analysis found the most important factors in differentiating likelihood of colonization vs. infection were recent prior hospitalization, history of wound debridement, and number of invasive procedures. Ten percent of (C) died and 25.5% of (I) died. MRSA contributed to death in 57.6% of the (I) deaths (p less than .05). These results underscore the importance of differentiating (C) vs. (I) in hospitals where MRSA is endemic so that early specific treatment may be initiated. Risk factors for infection should be discriminated from those for acquisition of the organism.