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TB Rate in South African Township Plummets After Antiretrovirals Arrive
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5th IAS Conference on HIV Pathogenesis, Treatment and Prevention, July 19-22, 2009, Cape Town
Mark Mascolini
"findings strongly suggest that bolstering the immune system of HIV-infected people with antiretroviral therapy helps protect them from TB and lowers TB prevalence. Because TB is the leading cause of death in HIV-infected people in many countries with high prevalence of both infections, the results add to arguments for extending antiretroviral therapy to more people in these regions, including those with CD4 counts above 200."
Tuberculosis prevalence in a township near Cape Town dropped from 3% in 2005 to 1.8% in 2008, during the years when South Africa began making antiretrovirals available to people with HIV [1]. Falling TB prevalence could be traced almost entirely to HIV-infected people.
Researchers compared HIV and TB rates in 2005 and 2008 in a clearly defined township whose residents all used the same medical clinic. The 2005 study recorded an overall TB prevalence of 3% and a 9% rate in people with HIV [2]. Most TB cases in people with HIV were not diagnosed until health workers tested people for the study.
The 2008 survey used methods similar to those used in 2005. To diagnose TB, health workers collected two sputum specimens from each person in a random population sample. They completed a TB history questionnaire for each person and used an oral assay to test everyone for HIV. The investigators defined undiagnosed TB as two positive smears, two positive cultures for Mycobacterium tuberculosis, or one positive smear plus one positive culture on separate specimens.
The 2005 population included 762 people (after a 15% refusal rate), while the 2008 survey included 1251 (after a 9% refusal rate). Median age stood at 27 in 2005 and 23 in 2008, while proportions of men were 45% and 52%. HIV prevalence was similar in 2005 (23%, 95% confidence interval [CI] 20% to 26%) and 2008 (25%, 95% CI 23% to 28%).
TB prevalence dropped from 3% (95% CI 2.0% to 4.5%) in 2005 to 1.8% (95% CI 1.0% to 2.5%) in 2008. In an analysis adjusted for age, gender, and HIV status, that decline was statistically significant (P = 0.012).
Previously diagnosed TB prevalence fell from 5.2% among 174 HIV-infected people in 2005 to 1.3% among 306 HIV-infected people in 2008, a statistically significant drop (P = 0.01). An already diagnosed TB prevalence of 4.0% in the 2005 HIV group fell to 2.3% in the 2008 HIV group, but that decline lacked statistical significance (P = 0.24). The overall TB case rate in people with HIV sank from 9.2% in 2005 to 3.6% in 2008, a significant decrease (P = 0.02).
In the HIV-seronegative groups of 584 people in 2005 and 899 in 2008, neither diagnosed nor previously undiagnosed TB rates fell significantly. Overall prevalence in the HIV-negative group was 1.2% in 2005 and 1.1% in 2008 (P = 0.98).
Although the investigators did not report how many HIV-infected people were taking antiretrovirals in 2008 versus 2005, the antiretroviral rollout seems to be the only plausible explanation of dwindling TB prevalence in this township. Three other possible explanations did not withstand scrutiny:
First, TB case-finding rates did not change much from 2005 to 2008 in people with or without HIV. Second, increased TB mortality did not explain the lower TB prevalence in 2008; in fact, TB-related mortality fell in this population from 2005 to 2008, particularly among people with HIV. Third, there was no evidence that people with TB moved out of the township between 2005 and 2008.
Although results in this single township may not apply to other South African or sub-Saharan populations, the findings strongly suggest that bolstering the immune system of HIV-infected people with antiretroviral therapy helps protect them from TB and lowers TB prevalence. Because TB is the leading cause of death in HIV-infected people in many countries with high prevalence of both infections, the results add to arguments for extending antiretroviral therapy to more people in these regions, including those with CD4 counts above 200.
References
1. Middelkoop K, Wood R, Myer L, et al. Widespread ART is associated with decline in TB prevalence. 5th IAS Conference on HIV Pathogenesis, Treatment and Prevention. July 19-22, 2009. Cape Town. Abstract WELBB105.
2. Wood R, Middelkoop K, Myer L, et al. Undiagnosed tuberculosis in a community with high HIV prevalence: implications for tuberculosis control. Am J Respir Crit Care Med. 2007;175:6-8.
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