Colonization sites of USA300 methicillin-resistant Staphylococcus aureus in residents of extended care facilities.

Background: The anterior nares are the most sensitive single site for detecting methicillin-resistant Staphylococcus aureus (MRSA) colonization. Colonization patterns of USA300 MRSA colonization are unknown.

Objectives: To assess whether residents of extended care facilities who are colonized with USA300 MRSA have different nares or skin colonization findings, compared with residents who are colonized with non-USA300 MRSA strains.

Methods: The study population included residents of 5 extended care units in 3 separate facilities who had a recent history of MRSA colonization. Specimens were obtained weekly for surveillance cultures from the anterior nares, perineum, axilla, and skin breakdown (if present) for 3 weeks. MRSA isolates were categorized as USA300 MRSA or non-USA300 MRSA.

Results: Of the 193 residents who tested positive for MRSA, 165 were colonized in the anterior nares, and 119 were colonized on their skin. Eighty-four percent of USA300 MRSA-colonized residents had anterior nares colonization, compared with 86% of residents colonized with non-USA300 MRSA (P= .80). Sixty-six percent of USA300 MRSA-colonized residents were colonized on the skin, compared with 59% of residents colonized with non-USA300 MRSA (P= .30).

Conclusions: Colonization patterns of USA300 MRSA and non-USA300 MRSA are similar in residents of extended care facilities. Anterior nares cultures will detect most--but not all--people who are colonized with MRSA, regardless of whether it is USA300 or non-USA300 MRSA.