Methicillin-resistant Staphylococcus aureus in a teaching hospital: investigation of nosocomial transmission using a matched case-control study

In early 1996 a hospital-wide methicillin-resistant Staphylococcus aureus ( MRSA) epidemic was recognized in a 900-bed university hospital. In order to investigate hospital-specific transmission routes, a case-control study wa s carried out. Cases and controls were matched for age (+/- years), sex, ad mission date (+/-10 days) and clinical department on admission. Data on pot ential risk factors, were retrieved by chart review. Between June 1996 and February 1997, 67 patients with hospital-acquired MRSA were identified. Mol ecular typing showed that 85% of the cases carried an indistinguishable str ain. The average time at risk for cases and controls was 17.3 and 23.7 days , respectively (P = 0.01). Seventeen patients (25.4%) developed infection. Conditional multivariate regression analysis showed that intensity of care (P = 0.002), number of transfers (P = 0.019), and fluoroquinolone therapy ( P = 0.025) were independently associated with acquisition of MRSA. Intensit y of care can be considered as a surrogate marker for a number of manipulat ions which represent the main risk factors for MRSA transmission. Frequent transfers within the hospital hinder, not only the epidemiological analyses , but also efforts to bring an outbreak under control. Our findings give ep idemiological support to recent molecular studies which suggest that fluoro quinolone use may increase the transmissibility of MRSA in hospitals. (C) 2 000 The Hospital Infection Society.