Screening for MRSA in ICU patients. How does PCR compare with culture?

The polymerase chain reaction (PCR) for the detection of methicillin-resistant Staphylococcus aureus (MRSA) has the potential to reduce the time before the identification of nasal carriage, and therefore help in the control and prevention of spread.

In a pilot study in a general intensive care unit (ICU) we compared culture with PCR for MRSA detection.

Between October and November 2005, 170 swabs taken from 63 patients on admission, and then twice weekly were cultured on Columbia Blood Agar, CHROMagar MRSA (CHROMagar Microbiology, Paris, France) and by enrichment and swaps were also tested for MRSA by real-time PCR, using the IDI-MRSA assay.

Five patients, previously not know to be positive for MRSA, were detected, but PCR detected only three of these initially. The quickest time to detection using culture was with CHROMagar MRSA, which detected 80% of MRSA. Real-time PCR was rapid (2.25 h) and facilitated the optimization of antibiotic therapy in two of three positive PCR patients, but PCR was less specific and more expensive than CHROMagar MRSA.

PCR facilitates the rapid detection of MRSA and has the potential to contribute to preventing spread, but should continue to be used in conjunction with culture.