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As health services move toward universal methicillin-resistant Staphylococcus aureus (MRSA) screening for hospital admissions, the most cost-effective approach is yet to be defined. In this study, one of the largest to date, we evaluated the performance of the BD GeneOhm MRSA assay on the Rotor-Gene 6000 thermal cycler, using samples taken directly from pooled MRSA screens. Results were compared with the same assay performed on the Smart-Cycler II platform and overnight broth culture. Samples yielding discrepant results were subjected to detailed analysis with an in-house PCR and patient note review. A total of 1,428 pooled MRSA screens were tested. Sensitivities and specificities of 85.3% and 95.8% for the Rotor-Gene and 81% and 95.7% for the Smart-Cycler were obtained, compared with broth enrichment. The sensitivity of the BD GeneOhm assay was increased to 100% when the results of in-house PCR and patient note review were taken into account. This study demonstrates that the Rotor-Gene 6000 thermal cycler is a reliable platform for use with the BD GeneOhm assay. It also proves that commercial PCR can be performed direct on pooled samples in selective broth, without the need for overnight incubation.

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SUMMARY A commercial M antibody capture ELISA kit (Rubenz M) for the detection of rubella specific IgM was evaluated in comparison with M antibody capture radioimmunoassay. A total of 248 sera were evaluated, including sera from cases of primary postnatal rubella, congenital rubella, infectious mononucleosis, and sera which contained rheumatoid factor. No false positive results were obtained but two high positive sera gave Rubenz M values which were below the value recommended as indicative of a positive result. We therefore propose changes in the criteria used for assessing the significance of the results obtained. These changes improve the accuracy of the assay without loss of specificity.The ability to detect rubella specific IgM is an essential requirement for the serological diagnosis of primary postnatal rubella as sera are often received too late in the evolution of the illness for diagnostic rises in total antibody titre or rubella specific IgG to be shown. Even when diagnostic rises in titre are shown, the demonstration of appreciable concentrations of rubella specific IgM indicates primary rubella rather than reinfection. This latter situation is particularly applicable to subclinical infections as a reinfection appears to be of minimal risk to the fetus.' Furthermore, the detection of rubella specific IgM in neonatal sera has become an established method of diagnosing congenital rubella.Several techniques are currently available for the detection of rubella specific IgM. Sera may be fractionated by sucrose density gradient ultracentrifugation2 or by gel filtration,3 with haemagglutination inhibition or immunofluorescent detection of rubella specific antibodies being performed on the fractions containing immunoglobulin. These techniques are time consuming, only limited numbers of sera may be evaluated, and technical problems occur such as the presence of residual non-specific inhibitors of haemagglutination. These assays are now being replaced by immunological assays that do not

Enteroviruses cause significant illness in man but viral diagnosis is problematic. Enterovirus-specific IgM tests have been developed but due to the difficulties of obtaining reliable control sera the interpretation of assay data remains mainly arbitrary and empirical. The present study was undertaken to assess the reliability of such assays by comparing two tests performed independently in two different laboratories: a mu-capture radioimmunoassay (MACRIA) which utilizes 35S-labelled Coxsackie virus antigens and an enzyme immunoassay (EIA). A feature of the MACRIA was that sera were tested in one large batch whereas the EIA was in routine use in a reference laboratory. The MACRIA was easy to perform but more suitable for research investigations than routine diagnostic use. Similar results were detected in the majority of sera tested in the two assays with 85% concordance achieved on testing 120 sera. Of the 18 discrepant results, 11 were positive by EIA only and 7 by MACRIA only. 89-95% concordance was obtained on testing sera against individual Coxsackie B1-5 serotypes, moreover 52% of the sera positive in MACRIA were reactive against only one viral antigen and the results on certain of the more strongly reactive sera suggested the existence of a measure of type specificity in the MACRIA test. Qualitative differences between the two tests highlighted problems of interpretation in the absence of a gold standard and cautioned against sole reliance on serology for diagnosis of enteroviral infections.

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