Validation of the IDI-MRSA system for use on pooled nose, axilla, and groin swabs and single swabs from other screening sites.

A commercial rapid polymerase chain reaction methicillin-resistant Staphylococcus aureus (MRSA) screening method (IDI-MRSA) is validated for the use with nasal swabs transported in liquid Stuart's medium. We investigated the use of IDI-MRSA for screening for MRSA in pooled nose, axilla, and groin swabs and in single swabs from skin puncture sites, wounds, throat, rectum, and groin using swabs transported in Amies medium without charcoal. We performed the IDI-MRSA test on swabs that had been used for routine MRSA broth culture and which were selected to be about 50% MRSA positive. We compared the IDI-MRSA result with the MRSA culture result. With 201 pooled sets, the sensitivity of IDI-MRSA was 85% and the specificity 95%. With 32 single screening swabs, sensitivity was 94% and specificity 80%. The method is not compromised by swab transport in Amies medium if an additional heating step is used. We had a low rate of initial inhibition (1.3%), which may have been due to the extra heating step used to liquefy gel from the Amies medium. Thus, in this study IDI-MRSA gives similar results to culture with pooled or single swabs from multiple screening sites.