A blinded comparison of three laboratory protocols for the identification of patients colonized with methicillin-resistant Staphylococcus aureus

OBJECTIVE: To compare three laboratory screening protocols for the detection of methicillin-resistant Staphylococcus aureus (MRSA) from surveillance specimens (mannitol-salt agar containing 2 mug/mL of oxacillin [MSA-2], mannitol-salt agar containing 4 mug/mL of oxacillin [MSA-4], and a broth-containing protocol as recommended by the American Society for Microbiology [M-AsM]). DESIGN: Blinded comparative laboratory study and cost analysis. SETTING: University-affiliated microbiology laboratory. METHODS: Outcome measurements included rate of detection of MRSA-positive specimens and patients, turnaround time, and media and technologist costs. Al MRSA culture swabs obtained from any patient site from November 1998 to April 1999 were included. RESULTS: The M-ASM protocol detected between 19.1% and 32.0% more MRSA-positive specimens and between 13.3% and 23.3% more MRSA-positive patients per surveillance event than the MSA-4 and MSA-2 protocols, respectively. There was no difference in positive-culture reporting lime between the M-ASM and MSA-4 protocols. The broth-containing protocol was 2- to 2.5-fold more expensive than the simpler protocols, taking into account media and laboratory personnel costs. CONCLUSIONS: It remains to be determined whether it is cost beneficial for a hospital to adopt the M-ASM, as the potential cost of MRSA transmission from unidentified MRSA-colonized patients is unknown. A broth-containing protocol should be considered the gold standard in future studies examining newer MRSA screening protocols.