Risk factors for methicillin-resistant Staphylococcus aureus (MRSA) acquisition in roommate contacts of patients colonized or infected with MRSA in an acute-care hospital

objective. To identify risk factors for acquisition of methicillin-resistant Staphylococcus aureus (MRSA) in patients exposed to an MRSA-colonized roommate. design. Retrospective cohort study. setting. A 472-bed acute-care teaching hospital in Toronto, Canada. patients. Inpatients who shared a room between 1996 and 2004 with a patient who had unrecognized MRSA colonization. methods. Exposed roommates were identified from infection-control logs and from results of screening for MRSA in the microbiology database. Completed follow-up was defined as completion of at least 2 sets of screening cultures (swab samples from the nares, the rectum, and skin lesions), with at least 1 set of samples obtained 7-10 days after the last exposure. Chart reviews were performed to compare those who did and did not become colonized with MRSA. results. Of 326 roommates, 198 (61.7%) had completed follow-up, and 25 (12.6%) acquired MRSA by day 7-10 after exposure was recognized, all with strains indistinguishable by pulsed-field gel electrophoresis from those of their roommate. Two (2%) of 101 patients were not colonized at day 7-10 but, with subsequent testing, were identified as being colonized with the same strain as their roommate (one at day 16 and one at day 18 after exposure). A history of alcohol abuse (odds ratio [OR], 9.8 [95% confidence limits {CLs}, 1.8, 53]), exposure to a patient with nosocomially acquired MRSA (OR, 20 [95% CLs, 2.4, 171]), increasing care dependency (OR per activity of daily living, 1.7 [95% CLs, 1.1, 2.7]), and having received levofloxacin (OR, 3.6 [95% CLs, 1.1, 12]) were associated with MRSA acquisition. conclusions. Roommates of patients with MRSA are at significant risk for becoming colonized. Further study is needed of the impact of hospital antimicrobial formulary decisions on the risk of acquisition of MRSA.