Clusters of new tuberculosis cases in North-West London: A survey from three hospitals based on IS6110 RFLP typing

Objectives: The relative contributions of reactivation of latent infection and clusters of new infections to the overall incidence of tuberculosis in the U.K. is unknown. A study was carried out in North-West London to determ ine the feasibility of IS6110 RFLP strain typing as a tool to investigate t he relative contributions of these two sources. Methods: All available isolates of M, tuberculosis from specimens collected over a calendar year at three participating hospitals were typed by RFLP u sing an IS6110 probe, Isolates exhibiting a single band pattern were subjec t to further typing using an oligonucleotide direct repeat probe. Demograph ic and clinical information on cases was obtained from the National Survey of Tuberculosis Notifications in England and Wales and further information sought on clustered cases as identified by RFLP typing. Results: Twenty-seven (23%) of the 118 cases had shared IS6110 RFLP pattern s, Strains From nine cases had single band patterns, but these were all dis tinguishable from each other when subjected to further typing by direct rep eat probe. The remaining 18 cases belonged to eight clusters, Epidemiologic al links were established between all the patients in each cluster, The lik elihood of being in a cluster was increased in cases with pulmonary smear-p ositive disease. It was lower in cases of Indian Sub-continent ethnic origi n. For 10 of the 18 clustered cases epidemiological links had not been esta blished by conventional contact tracing. Conclusions: Investigation of the relative contributions of reactivation of latent infection and new infection is feasible in a UK population, using I S6110 RFLP typing of M. tuberculosis isolates and epidemiological enquiries , This study in London identified clustered, presumably new cases, the majo rity of whom had not been linked epidemiologically. Comprehensive IS6110 RF LP typing of UK isolates would probably identify many clusters of incident tubercular infection, (C) 2000 The British Infection Society.