The impact of antiretroviral therapy on tuberculosis incidence

Introduction Although HIV infection increases the likelihood of developing TB, evidence suggests that starting ART reduces the risk of TB incidence although not to the level of HIV negative people in the population. This study aims to determine the impact of ART on TB incidence in people living with HIV in the Western Cape Province of South Africa. Methods This is a retrospective cohort study using routinely collected data of HIV infected individuals aged 15 years and above from public health facilities in the Western Cape Province, South Africa, between 2007 and 2016. A Marginal Structural Model (MSM) with inverse probability of treatment weighting (IPTW) was used to estimate the effect of ART on TB incidence adjusting for measured time-dependent confounding by CD4 count. Results ART was associated with a 77.3% (95% CI, 76.7% – 78.0%) reduction in the risk of TB incidence in HIV infected patients. The overall TB incidence was 9 855 per 100 000 patient years (95% CI, 9 798 – 9 912). Patients on ART and those not on ART had a TB incidence of 3 939 and 15 329 per 100 000 patient years respectively. TB incidence was higher in males than females, and higher in patients with lower CD4 count at baseline and during follow-up. TB incidence declined with increasing ART duration and rising CD4 count but remained elevated compared to background incidence. Conclusion This study has shown that ART is highly effective at preventing TB in people living with HIV. The recent introduction of universal ART access for everyone living with HIV should contribute to further reducing TB incidence in South Africa and other high HIV and TB burden countries.