Laboratory reports of opportunistic and other mycobacterial infections and their relationship to notifications of tuberculosis in England and Wales

Setting: England and Wales, UK. Objective: To investigate: (1) whether misclassification of opportunistic mycobacterial disease had contributed to the failure of tuberculosis notifications to continue declining; (2) whether laboratory reports of Mycobacterium tuberculosis complex infections could be used to validate trends in the tuberculosis notification system. Design: Descriptive epidemiological study using laboratory reports of infections to the Public Health Laboratory Service Communicable Disease Surveillance Centre, Medical Research Council National Surveys of Tuberculosis and tuberculosis notifications to the Office of Population Censuses and Surveys. Results: Compared to 1983, an extra 1% of tuberculosis notifications in 1988 were opportunistic mycobacterial disease inappropriately notified as tuberculosis. On the basis of the expected proportion of microbiologically confirmed tuberculosis infections, laboratory reporting was incomplete: for one laboratory report there were four notifications. Conclusion: Misclassification of opportunistic mycobacterial infection was estimated to account for only a small proportion of the excess tuberculosis notifications since 1988. This excess of tuberculosis notifications could be due to artefact, for instance because a greater proportion of cases are being notified. Laboratory reports of tuberculosis infections are of limited use in validating the recent trends in tuberculosis notification rate. At present changes in the level of reporting of laboratory isolates are likely to obscure genuine trends.