Epidemiology of Nosocomial Infections Caused by Methicillin-Resistant <i>Staphylococcus aureus</i>

TLDR

Hospital-acquired MRSA infections are increasingly frequent in the United States. Infected and colonized inpatients are the main reservoir, with transient hand carriage by staff driving patient-to-patient transmission, a finding confirmed by a university hospital outbreak control program that used surveillance of colonized and infected patients. Two thirds of MRSA outbreaks occur in critical care units, and in over 85 % of hospitals the organism becomes endemic; surveillance identified 38 %, 31 %, and 31 % of new cases via daily labs, monthly surveys, and rehospitalization, and control measures reduced prevalence and acquisitions over 12 months.

Abstract

Outbreaks of hospital-acquired infections caused by methicillin-resistant Staphylococcus aureus are being recognized with increasing frequency in the United States. Two thirds of outbreaks have been centered in critical care units. Infected and colonized inpatients appear to be the major institutional reservoir, and 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 three 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-month period.