Evaluation of methods and costs for detecting methicillin-resistant Staphylococcus aureus isolates from clinical specimens at regional hospitals in Trinidad and Tobago.

ABSTRACT

OBJECTIVES: To evaluate and determine the most cost effective, rapid and specific method for detection of methicillin resistance in clinical isolates of S. aureus in a setting with limited personnel and resources. METHODS: Standard laboratory methods were used to identify S. aureus isolates. The conventional Methicillin Resistance Staphylococcus aureus (MRSA) detection methods used included, 1 microg oxacillin disk diffusion, oxacillin salt agar screen (CLSI), penicillin binding protein (PBP 2') latex agglutination test and E-tests oxacillin. Results of conventional tests were compared with a polymerase chain reaction (PCR) method for detecting MRSA isolates. Polymerase chain reaction detection of the mecA gene in S. aureus was used as the "gold standard" for MRSA identification. RESULTS: All methods had 100% sensitivity except for oxacillin disk diffusion and oxacillin-salt agar screening with 98% and 99%, respectively. Specificity was also 100% for all methods except for oxacillin-disk diffusion (99%). Turn around time (TAT) for detection of MRSA was calculated to be within six hours for PCR. The fastest TAT of 1.25 hours was obtained for PBP 2' latex agglutination. Total cost for labour and materials to perform each method was highest for E-test, US$13.76/isolate. The cost for PCR when compared to that of latex agglutination was not statistically significant (US$3.74 vs US5.91, p = 0.4). CONCLUSIONS: All methods presented high sensitivity and specificity, but the latex agglutination test had the advantage of giving a reliable, rapid and most cost effective result that compares well to PCR in this environment.