The laboratory could decide on the procedure as long as optical control was performed to confirm freezing. In the GeneXpert study the Xpert MRSA assay run on a 4-site GeneXpert? system (Cepheid, Sunnyvale, sellekchem CA USA) was used in accordance with manufacturers’ protocol. Nose, throat and perineum specimen were processed separately, and additional specimens, when present, were pooled in the fourth cartridge.On a patient level, PCR-based screening results were considered positive if at least one PCR result was positive and were considered negative if the nasal swab and at least one other test result were negative (and the other sites negative or non-conclusive). In case of a non-conclusive PCR result of the nasal swab, the overall test result for that patient was considered non-conclusive and isolation was continued until conventional cultures were negative or until a second PCR test performed on a new nasal swab was negative.

Results, both positive and negative, were immediately reported to the wards. MRSA PCR was performed within 24 hours on working days, and not in weekends and on holidays (except for five hospitals during the GeneXpert study). Final results of conventional cultures were considered as the gold standard. Therefore, isolation measures based upon a positive PCR result were withdrawn when conventional culture results were negative.Statistical analysisTest characteristics were determined at the patient level based on a combination of the results from all anatomical sites sampled. For determination of test characteristics patients were either MRSA negative (including those with non-conclusive results) or positive.

Continuous variables were compared using the Mann-Whitney U test; categorical variables were compared with the ��2 test and Fisher exact test. All analyses were performed using SPSS.ResultsPatient population and test characteristicsA total of 163 patients were included yielding 941 screening samples (163 nares, 163 throat, 163 perineum, 129 wound, 85 urine, 52 sputum, 186 catheter insertion sites, drains and other samples): 5.8 sites were tested per patient. Eighty-nine patients were screened with BD GeneOhm? MRSA PCR (Figure (Figure1)1) and 74 with Xpert MRSA assay (Figure (Figure2).2). In total 787 MRSA PCRs were performed, 519 (5.8 per patient, all specimens processed separately) and 268 (3.

6 per patient, including pooled specimens) in the IDI and GeneXpert studies, respectively. Numbers of patients included per hospital ranged from 1 to 57. Contact with an MRSA carrier was the Batimastat most important reason for screening (Table (Table2).2). The prevalence of MRSA carriage, based upon conventional microbiological cultures, was 3.1% (n = 5 patients), with the highest carriage rate among those screened because of contact with pigs.