January 07, 2014
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Advanced HIV immunosuppression prevented TB transmission to household contacts

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People with tuberculosis who had advanced HIV immunosuppression were less likely to transmit tuberculosis to household contacts, researchers from Harvard University have found.

“Our results suggest that HIV-induced immunosuppression reduces the risk of TB transmission from HIV co-infected index cases within households,” the researchers wrote in Clinical Infectious Diseases. “Possible biological explanations are that immunosuppressed patients are infectious for shorter periods of time and that the reduced TB bacillary load and tissue destruction typical of late stage HIV reduced the likelihood of spread.”

From September 2009 to August 2012, the researchers identified 1,608 index patients with drug-sensitive TB and 4,841 exposed household contacts who had no history of TB. The prevalence of HIV in the TB cases was 3%. Among the household contacts, the prevalence of TB was 44.99% in adults and 22.07% in children.

In a multivariate analysis, the risk of a positive tuberculin skin test was higher in household contacts who were close relatives of the index case (RR=1.47; 95% CI 1.28-1.7 for a child; RR=1.17; 95% CI, 1.01-1.32 for a sibling; and RR=1.38; 95% CI, 1.18-1.56 for a spouse). If the TB case with HIV had a CD4 count of less than 250 cells/mcL, then the household contacts were less likely to be infected than those of HIV-negative TB cases (RR=0.49; 95% CI, 0.24-0.96). For children younger than 15 years, none who were exposed to HIV-positive cases with CD4 counts of less than 250 cells/mcL were infected with TB vs. 22% of those exposed to non-HIV-infected TB cases.

Disclosure: The researchers report no relevant financial disclosures.