Improving surveillance of MRSA bacteraemia

Editor—Wyllie et al recommend that on admission, accounting for 24% of all MRSA bacteraemias, require immediate consideration for vancomycin treatment.¹

We investigated all positive blood cultures taken in acute admissions at this hospital over three years. We used microbiology laboratory results, case notes, notes taken by the infection control nurses, and reports to Health Protection Scotland of bloodborne infections to determine whether these infections were genuine.

The total number of S aureus bacteraemias was 244, with 65 in acute admissions. The number of MRSA bacteraemias was 112, with 24 in acute admissions, which accounted for 18.8% of all hospital MRSA bacteraemias. Seventeen patients (81%) had been admitted from a nursing home or other hospital or had recently had an inpatient hospital stay (less than 6 months previously). The contamination rate from all blood cultures for accident and emergency was 49% over the three years.

A significant proportion (50%) of MRSA from blood cultures, in patients newly admitted to hospital, were not suggestive of generalised infection. The source of the MRSA could be skin colonisation of the patient contaminating the blood cultures, or even the medical or nursing staff taking the blood cultures in the hectic environment of acute admissions. The 49% contamination rate for all blood cultures in accident and emergency further supports these results.

These data highlight that blood culture results should be interpreted in context with the patient's general condition, subsequent progress, and MRSA status determined by screening.