Epidemiology of Nosocomial Infections Caused by Methicillin-Resistant Staphylococcus aureus

Abstract

Outbreaks of hospital-acquired infections caused by methicillin-resistant S. aureus are being recognized with increasing frequency in the USA. Two thirds of the outbreaks have been centered in critical care units. Infected and colonized inpatients appear to be the major institutional reservoir; transient carriage on the hands of hospital personnel appears to be the most important mechanism of serial patient-to-patient transmission. In over 85% of hospitals into which they have been introduced, methicillin-resistant strains of S. aureus have become established as endemic nosocomial pathogens. A program designed to control a widespread outbreak in a university hospital used 3 surveillance methods to identify the major institutional reservoir of colonized and infected inpatients. Daily clinical laboratory surveillance, monthly prospective microbiologic surveys of high-risk inpatients and the recognition of previously infected or colonized patients at rehospitalization identified 38%, 31% and 31% of new cases, respectively. After control measures were instituted, the prevalence (P < 0.001) and the number of acquisitions (P < 0.002) of methicillin-resistant S. aureus declined over a 12 mo. period.