The control of meticillin-resistant Staphylococcus aureus (MRSA) is a global healthcare priority. Screening patients for MRSA carriage occupies a central position in this control. Conventional culture methods for MRSA screening take 2-3 days to produce a positive result. Polymerase chain reaction (PCR) based systems can detect MRSA within one day ('rapid screening') though these tests are more costly than culture tests. It is hypothesised that rapid detection of MRSA carriers will lead to faster implementation of control procedures, reducing the transmission of MRSA. The first study in this thesis validates a rapid method, IDI-MRSA ™ for use on pooled and non-nasal specimens. The second paper is a controlled trial of the IDI-MRSA™ test. It investigated whether rapid MRSA screening leads to a reduction in MRSA acquisition and was set on ten wards of a London teaching hospital. The main outcome was the MRSA acquisition rate (proportion of patients negative for MRSA who became MRSA positive). Secondary outcomes included test characteristics and measures of resource use. The intervention was PCR screening for MRSA compared with conventional culture. 6888 (82.3%) patients had full data. The overall MRSA carriage rate on admission was 6.7%. Rapid tests led to a reduction in median reporting time from admission (46 to 22 hours, P<0.001) and reduced the number of inappropriate pre-emptive isolation days between the two arms (399 v 277, P<0.001). 108 (3,2%) patients in the control arm and 99 (2.8%) in the intervention arm acquired MRSA. When confounding factors were taken into account the adjusted odds ration was 0.91 (95% confidence interval 0.61 to 1.234). Rates of MRSA transmission, wound infection, and bacteraemia were not statistically different between the two arms. On these data it is unlikely that the increased costs of rapid tests can be justified compared with alternative control measures against MRSA.
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