Mixture analysis of tuberculin survey data from northern Malawi and critique of the method.


Davies, GR; Fine, PE; Vynnycky, E; (2006) Mixture analysis of tuberculin survey data from northern Malawi and critique of the method. The international journal of tuberculosis and lung disease, 10 (9). pp. 1023-9. ISSN 1027-3719

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Abstract

SETTING: Various methods have been used to estimate the prevalence of Mycobacterium tuberculosis infection from tuberculin survey data. All are complicated by prior sensitisation to environmental mycobacteria and bacille Calmette-Guérin (BCG) vaccination. Mixture analysis has recently been proposed as a means of overcoming misclassification and improving infection prevalence estimates. OBJECTIVE: To compare conventional and mixture model estimates of M. tuberculosis infection prevalence. DESIGN: Mixture models with two or three univariate normal components were fitted to the results of 53 909 tuberculin tests conducted in northern Malawi during 1980-1984. Data were stratified by BCG status, sex and age and corrected for digit preference. Prevalence estimates derived from mixture models were compared with those of conventional methods. RESULTS: The optimal model was age-dependent, with three- and one-component solutions preferred in younger and older age groups, respectively. In contrast with findings from elsewhere, a component corresponding to BCG vaccination was indistinguishable from that attributable to environmental mycobacterial exposure, and infection prevalence estimates in younger individuals with a BCG scar were inflated, irrespective of the method used. CONCLUSION: The validity of infection prevalence and incidence estimates based on mixture modelling is probably locale-dependent, and the assumptions underlying mixture models may not realistically reflect underlying immunological processes.

Item Type: Article
Faculty and Department: Faculty of Epidemiology and Population Health > Dept of Infectious Disease Epidemiology
Research Centre: TB Centre
PubMed ID: 16964795
Web of Science ID: 240012200015
URI: http://researchonline.lshtm.ac.uk/id/eprint/11378

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