Detection of methicillin-resistant Staphylococcus aureus in a low-prevalence setting by polymerase chain reaction with a selective enrichment broth.

The objective of this study was to evaluate the test characteristics of a modified BD GeneOhm methicillin-resistant Staphylococcus aureus (MRSA) assay on individual and pooled samples in a setting of low MRSA prevalence. The results of the polymerase chain reaction (PCR) assay were compared with culture results from a selective phenol red mannitol broth subcultured after 48 h. Sensitivity, specificity, and positive and negative predictive values (PPV and NPV, respectively) were calculated. For individual testing, 581 samples from 201 persons were collected; 18 (3.2%) were MRSA culture positive. Five hundred ten broths from 174 persons were combined in 106 pools after overnight incubation; 8 pools (7.5%) contained 1 or more MRSA culture-positive specimens. There were no inhibited PCR tests. The combined sensitivity of individual and pooled specimens was 92% (95% confidence interval [CI], 73-99%), the specificity was 98% (95% CI, 96-99%), and the PPV and NPV were 63% and 99.7%, respectively. Our modified procedure gives satisfactory results, and the pooling of broths may reduce costs.