TB transmission halved when CD4 count lies under 250 in Lima, Peru
HIV-positive people with a CD4 count at or below 250 cells/µL proved half as likely to transmit tuberculosis to household contacts as HIV-negative people in Lima, Peru. But HIV-positive people with a higher CD4 count transmitted TB to household partners as often as HIV-negative people.
Because previous research disagreed on TB transmission risk from HIV-positive people with TB, researchers in Lima, the capital of Peru, conducted this comparison between HIV-positive people and negative people between September 2009 and August 2012. The analysis involved 1608 people with drug-sensitive TB and 4841 of their household contacts.
A 2007-2008 study of people seeking HIV testing in Lima recorded an overall HIV prevalence of 3.2% and a prevalence of 10.5% in men who have sex with men (Clark JL, et al. Sexually Transmitted Infections. 2010; 86; 545-547).
Researchers tested TB patients for HIV, measured their CD4 count, and assessed their TB risk factors. They also recorded TB risk factors specific to the household and to exposed people in the household. Household contacts got tested for TB with the tuberculin skin test.
Statistical analysis adjusted for TB risk factors determined that household contacts of HIV-positive TB patients with a CD4 count at or below 250 cells/µL had a 50% lower risk of testing TB-positive than contacts of HIV-negative TB patients (risk ratio 0.49, 95% confidence interval 0.24 to 0.96). No children under 15 years old picked up TB upon exposure to an HIV-positive person with a CD4 count at or below 250 cells/µL, compared with 22% of children exposed to HIV-negative people.
Household TB transmission risk did not differ significantly between HIV-positive and negative people when the HIV-positive person had a CD4 count above 250 count cells/µL.
Notably, when an HIV-positive person with a CD4 count below 250 cells/µL becomes infected with Mycobacterium tuberculosis, TB has faster progression than in someone with a higher CD4 count (Martinson NA, et al. Epidemiology ot tuberculosis and HIV. Proceedings of the American Thoracic Society. 2011; 8: 288-293).
Source: Chuan-Chin Huang, Eric Tchetgen Tchetgen, Mercedes C. Becerra, Ted Cohen, Katherine C. Hughes, Zibiao Zhang, Roger Calderon, Rosa Yataco, Carmen Contreras, Jerome Galea, Leonid Lecca, Megan Murray. The effect of HIV-related immunosuppression on the risk of tuberculosis transmission to household contacts. Clinical Infectious Diseases. 2014; 58: 765-774.
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Source: IAS
