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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 …