The value of multiple surveillance cultures for methicillin-resistant Staphylococcus aureus

We evaluated our experience in a low prevalence setting to determine the extent to which multiple swabs increased detection rates and the incremental costs of doing so.

Nasal and groin swabs submitted in pairs were cultured onto a single plate (Oxoid MRSA Denim Blue Agar; Oxoid Company, Napean, ON, Canada). We determined whether MRSA was detected when swabs submitted in the preceding 3 days were negative. We explored the costs associated with screening and of each additional colonized patient detected.

In all, 60,049 paired nose and perineal swabs were submitted from 21,599 patients. In all, there were 12,750 duplicate, 1437 triplicate, and 112 instances when >4 swabs were processed within 3 days. The first culture was positive in 106 of 12,750 (0.83%%), 42 of 12,750 (0.33%) on the second when the first was negative, 7 of 1642 (0.43%) on the third or subsequent swab pair when the preceding 2 were negative.

Overall, the sensitivity of the first of multiple cultures of a set was 74.3%. Had the 14,392 multiple samples not been submitted, 49 colonized patients would not have been identified. Additional laboratory costs associated with multiple samples equaled $2088 per patient identified.