Colonization by Staphylococcus aureus Resistant to Methicillin and Ciprofloxacin during 20 Months' Surveillance in a Private Skilled Nursing Facility

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Abstract
Objective: To evaluate endemic colonization with Staphylococcus aureus resistant to methicillin, ciprofloxacin, or both among patients of a private skilled nursing facility, with regard to colonization rate and site, and relation to infection and prior antibiotic use. Design: Prospective quarterly culture surveillance of nares and rectal specimens over 20 months' observation. Results: The mean prevalence was 3.8% in new admissions and 5.4% for in-house patients; cumulatively, 7.5% of the patients were colonized during the study period. The colonization rate remained stable during the study period. Screening of rectal, as well as nares, specimens detected substantially more colonized patients than would have been detected by nasal cultures alone. Five to seven percent of the colonized patients developed later infection with methicillin-ciprofloxacin-resistant S aureus. Colonized patients did not differ significantly from the noncolonized group in prior use of quinolones, but the colonized group was exposed significantly more frequently to other antibiotics than the noncolonized group. Eightythree percent of methicillin-resistant S aureus (MRSA) isolated from infections and 89% from colonization were also ciprofloxacin resistant. Conclusion: Although all infecting and most colonizing isolates of MRSA were resistant to quinolones, the overall rate of colonization remained low and stable despite the continued use of quinolones. The findings suggest that good infection control practice has prevented broader spread of such strains in this facility.