TB incidence lower with ART in rich countries, but not at age 50+
Tuberculosis incidence was 44% lower in HIV-positive people in high-income countries who started antiretroviral therapy (ART) than in those who did not. But the protective effect of ART did not extend to people older than 50 or with a CD4 count below 50 cells/μL.
Much research on the impact of ART on TB comes from low- and middle-income countries. This HIV-CAUSAL Collaboration involved 65,121 antiretroviral-naive people in 12 cohorts from the United States and Europe. No one had AIDS and everyone was 18 or older.
The researchers excluded 206 people diagnosed with TB within the first month of follow-up to prevent inclusion of patients with prevalent TB instead of incident TB. Follow-up extended from 1996 through 2007.
Over a median follow-up of 28 months, TB developed in 712 people to yield an incidence of 3.0 cases per 1000 person-years. Overall TB risk was 44% lower in people who started ART than in those who did not (hazard ratio [HR] 0.56, 95% confidence interval [CI] 0.44 to 0.72).
But TB incidence was not lower in people over 50 who started ART than in those who did not (HR 1.04, 95% CI 0.64 to 1.68) or in people with a time-updated CD4 count under 50 cells/μL (HR 1.46, 95% CI 0.70 to 3.04).
TB risk was marginally higher in people who had started ART less than 3 months ago (HR 1.36, 95% CI 0.98 to 1.89) but 56% lower in people who started ART 3 or more months ago (HR 0.44, 95% CI 0.34 to 0.58).
Compared with people who had not begun ART, hazard ratios for incident TB varied by age and by whether the latest CD4 count was below 50:
• Under 35 years old: HR 0.67 (95% CI 0.38 to 1.18)
• 35 to 50 years old: HR 1.51 (95% CI 0.98 to 2.31)
• Over 50 years old: HR 3.20 (95% CI 1.34 to 7.60)
• CD4 count under 50: HR 2.30 (95% CI 1.03 to 5.14)
The HIV-CAUSAL team concludes that “combined ART reduced tuberculosis incidence by half” in their cohort. But “increases in tuberculosis incidence shortly after combination ART, especially in those more than 50 years old and those with CD4 cell counts below 50 cells/μL, suggested unmasking immune reconstitution inflammatory syndrome.”
Source: The HIV-CAUSAL Collaboration. Impact of antiretroviral therapy on tuberculosis incidence among HIV-positive patients in high-income countries. Clinical Infectious Disease. 2012; 54: 1364-1372.
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