Evaluation of a real-time polymerase chain reaction assay using analyte-specific reagents for detection of methicillin-resistant Staphylococcus aureus nasal carriage.

Objective: To validate a real-time polymerase chain reaction (PCR) assay for the detection of methicillin-resistant Staphylococcus aureus (MRSA) that is capable of accommodating 30 patient samples in a single batch without compromising the level of sensitivity and specificity associated with PCR testing.

Study Design: A real-time PCR analyte-specific reagent (ASR) assay was compared to conventional culture methods using dual swab samples collected from the nares of 151 patients.

Results: Of the 151 specimens, 49 (32%) were positive for MRSA by PCR, whereas 40 (26%) were positive by culture methods. The Roche LightCycler 2.0 (Roche Diagnostics, Indianapolis, Indiana, U.S.A.) and its associated ASRs were capable of analyzing 30 patient samples and 2 controls in < 2 hours. Current data suggest that 4-10% of our patient specimens harbor both coagulase negative Staphylococcus and S aureus in the same sample. Samples such as this are reflexed to culture, only 24% of which contain MRSA. Efficiency in the laborato-ry was greatly improved. The sensitivity, specificity, positive predictive value and negative predictive value were 100%, 92%, 82% and 100%, respectively.

Conclusion: The Roche LightCycler 2.0 PCR platform is a sensitive and efficient screening method for determining the nasal carriage of MRSA with a rapid turnaround time in the clinical laboratory.