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The Effects of HIV Infection on TB

Genotypic clusters of TB including 1 HIV-infected person were larger, lasted longer, and had shorter periods between cases than did those involving only HIV-uninfected persons.

HIV infection has multiple effects on the natural history of TB — for example, it increases the risks for reactivation of latent infection and for exogenous infection. To quantify such effects, researchers analyzed data from a prospective 12-year (1991–2002) molecular epidemiologic study of TB in San Francisco.

A total of 2189 patients with culture-positive TB had restriction-fragment–length polymorphism (RFLP) genotyping performed on their isolates and had identified source cases. Of these isolates, 1593 were unique by RFLP analysis, and 596 were clustered. Among isolates from HIV-infected patients, 161 of 390 (41%) were part of clusters and were presumed to represent secondary transmission, compared with only 278 of 1799 isolates (15%) in the HIV-uninfected group (P<0.0005). Of the 158 genotypic clusters, those that included at least one HIV-infected patient were significantly larger than those involving only HIV-uninfected patients (median, 3 vs. 2 patients; P<0.00005). In addition, the median cluster duration was longer (243 vs. 96 days; P=0.009) and the median time between successive cases was shorter (57 vs. 79 days; P=0.018) in clusters including 1 HIV-infected patient than in those involving only HIV-uninfected patients. An estimated 405 cases of active TB were attributable to HIV infection; 73% of these cases occurred before 1997.

Comment: This study provides hard numbers concerning the effect of HIV infection on TB and documents the impact of secondary spread by HIV-infected persons. The good news is that the number of TB cases attributable to HIV infection dropped markedly after the introduction of potent combination antiretroviral therapy.

— Neil M. Ampel, MD

Published in Journal Watch Infectious Diseases November 21, 2007

Citation(s):

DeRiemer K et al. Quantitative impact of human immunodeficiency virus infection on tuberculosis dynamics. Am J Respir Crit Care Med 2007 Nov 1; 176:936.

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