Molecular epidemiology of HIV-associated tuberculosis in Dar es Salaam, Tanzania: strain predominance, clustering, and polyclonal disease

Abstract

Molecular typing of Mycobacterium tuberculosis can be used to elucidate the epidemiology of tuberculosis, including the rates of clustering, the frequency of polyclonal disease, and the distribution of genotypic families. We performed IS6110 typing and spoligotyping on M. tuberculosis strains isolated from HIV-infected subjects at baseline or during follow-up in the DarDar Trial in Tanzania and on selected community isolates. Clustering occurred in 203 (74%) of 275 subjects: 124 (80%) of 155 HIV-infected subjects with baseline isolates, 56 (69%) of 81 HIV-infected subjects with endpoint isolates, and 23 (59%) of 39 community controls. Overall, 113 (41%) subjects had an isolate representing the East Indian "GD" family. The rate of clustering was similar among vaccine and placebo recipients and among subjects with or without cellular immune responses to mycobacterial antigens. Polyclonal disease was detected in 6 (43%) of 14 patients with multiple specimens typed. Most cases of HIV-associated tuberculosis among subjects from this study in Dar es Salaam resulted from recently acquired infection. Polyclonal infection was detected and isolates representing the East Indian GD strain family were the most common.

Fig 1

Diagram of M. tuberculosis isolate evaluation. This figure describes the breakdown of subjects and their isolates by category (screened subjects with baseline isolates, enrolled subjects with endpoint isolates, and community subjects with control isolates) included in the analysis and the degree of clustering and East Indian GD family representation in each. Baseline isolates were obtained from HIV-infected subjects when screened for the DarDar Vaccine Trial; endpoint isolates were obtained from enrolled HIV-infected subjects at the time of a tuberculosis diagnosis. Superscripts: a, uninterpretable results were mostly the result of mixed cultures caused by contamination or representative of a mixed infection; b, twelve duplicate results from nine subjects with multiple specimens were removed from the main analysis but included in the determination of polyclonal disease; c, includes one polyclonal disease subject with two isolates; d, includes five polyclonal disease subjects with two isolates each.

Fig 2

M. tuberculosis strains from the study subjects in a phylogenetic framework. This figure depicts the evolutionary phylogenic tree of M. tuberculosis strain families and the number of isolates from each identified in our study population. RFLP, restriction fragment length polymorphism. A total of 327 isolates were examined, including 281 RFLP results from 275 subjects (one isolate per subject included in the analysis except for two isolates per subject for six subjects with polyclonal disease), 204 clustered isolates (from 203 subjects), and 77 nonclustered isolates (from 72 subjects).