Objective: The objective of this study is to estimate the effectiveness of antiretroviral treatment (ART) in preventing tuberculosis (TB) in HIV-infected people during the first 6 years of ART programme expansion.
Design: A cohort study comparing TB risk without ART and after ART initiation.
Setting: Public sector HIV programme of the Free State province, South Africa.
Participants: Seventy-four thousand and seventy-four HIV-infected people enrolled from 2004 until 2010, of whom 43 898 received ART and 30 176 did not.
Intervention: Combination ART.
Main outcome measures: Time to first TB diagnosis, adjusted for CD4 cell count, weight, age, sex, previous TB, district and year, with ART, CD4 cell count and weight as time-varying covariates and with death as a competing risk.
Results: Three thousand eight hundred and fifty-eight first TB episodes occurred during 78 202 person-years at risk with ART and 5669 episodes occurred during 62 801 person-years without ART [incidence rates 4.9 and 9.0 per 100 person-years, crude incidence rate ratio 0.55 (95% confidence interval 0.52-0.57)]. The adjusted subhazard ratio (SHR) of time to first TB episode after starting ART, compared with follow-up without ART, was 0.67 (0.64-0.70). Within CD4 cell count subgroups (<50, 50-199, 100-199, 200-349 and >350 cells/μl), the respective SHRs were 0.64 (0.57-0.71), 0.63 (0.57-0.70), 0.66 (0.61-0.72), 0.67 (0.62-0.72), 0.72 (0.63-0.83) and 0.97 (0.60-1.59). Adjusted SHRs for ART decreased with each year of enrolment, from 0.90 (0.77-1.04) in 2004 to 0.54 (0.43-0.67) in 2010.
Conclusion: ART was effective in preventing TB in HIV-infected patients with CD4 cell counts below 350 cells/μl, but less so than previously estimated. Effectiveness increased each year.