Comparison of protocols for surveillance of methicillin-resistant Staphylococcus aureus (MRSA): medical staff vs ICU patients.

To compare the sensitivity of various protocols for methicillin-resistant Staphylococcus aureus (MRSA) surveillance, active surveillance for detecting MRSA nasal colonization was performed on 97 members of the medical staff and 218 patients in the Intensive Care Unit (ICU) of a university hospital. Duplicate nasal swabs were collected from each participant. One was plated directly on a blood agar plate (D-BAP) and observed at 24 and 48 hr. Another was incubated overnight in tryptic soy broth (TSB) with 6.5% NaCl, and subcultured on both BAP (B-BAP) and mannitol salt agar with 4 mg/L of oxacillin (B-MSAOXA). The MRSA colonization rate was similar in the medical staff and patient samples (16.5% vs 11.9%, p = 0.285). Among the medical staff members, the sensitivity of MRSA detection was the same (93.8%) in D-BAP and B-BAP. In the ICU patients, which are a high-risk group, the sensitivity of MRSA detection was improved by adding a pre-enrichment step (73.1% on D-BAP vs 96.2% on B-BAP). The simple direct plating protocol was sufficiently sensitive for the medical staff members, but pre-enrichment was an essential step to increase detection of MRSA in the ICU patients.