Effect of delayed infection control measures on a hospital outbreak of methicillin-resistant Staphylococcus aureus

All patients positive for methicillin-resistant Staphylococcus aureus (MRSX ) at the University Hospitals of Geneva, Switzerland, between 1989 and 1997 (N=1771) were included in a cohort study to evaluate the consequences of d elayed containment of a hospital-wide outbreak occurring during a LC-year a bsence of MRSA control measures. The effects of efforts to control both the MRSX reservoir and the number of bacteraernic patients were assessed. Inte nsive infection control measures were initiated in 1993 and included patien t screening, on-site surveillance, contact isolation, a computerized alert system, and hospital-wide promotion of hand hygiene. An increase in the rat e of new MRSA-infected or -colonized patients was observed between 1989 and 1994 (from 0.05 to 0.60 cases per 100 admissions), which subsequently decr eased to 0.24 cases in 1997 (P<0.001). However, the proportion of laborator y-documented methicillin-resistant isolates among all S. aureus showed litt le variation in the years from 1993 onwards (range, 19-24%), reflecting the result of an increase in the number of screening cultures. The annual numb er of patients with MRSA bacteraemia strongly correlated with the hospital- wide prevalence of MRSA patients (R-2 = 0.60; P= 0.01) and the rate of new MRSX patients (R-2 = 0.97; P< 0.001). Consequently; the attack rate of noso comial MRSA bacteraemia served as an excellent marker for the MRSX patient reservoir. In conclusion, despite delayed implementation, infection control measures had a substantial impact on both the reservoir of RIRSA patients and the attack rate of MRSA bacteraemia. (C) 2000 The Hospital Infection So ciety.