Comparison of effects of isoniazid plus ART and ART only regimen on the incidence of tuberculosis and HIV progression in HIV positive patients: a retrospective cohort study at two hospitals in Addis Ababa, Ethiopia.

Background: Tuberculosis is a major opportunistic complication of HIV-infection. Antiretroviral therapy (ART) lowers incidence of tuberculosis (TB) but may not be sufficient to control HIV-related tuberculosis, implying a need for additional interventions. The aim of this study was to compare the effects of isoniazid preventive therapy (IPT) plus ART and ART only regimens on the incidence of active TB and HIV progression in HIV positive patients. Methods: The retrospective cohort study was conducted at Tikur Anbessa Specialized Hospital and Zewditu Memorial Hospital on 185 patients receiving IPT plus ART and 557 patients receiving ART only. Incidence rates (IR) were used to determine incidence rates of tuberculosis. Time to AIDS and TB event were compared using student t-test. Risks of the outcomes were identified using regression models. Results: The study showed a reduced tuberculosis incidence rate from 7.44 to 1.8 cases/100 person-years [PYs] by IPT plus ART compared to ART only. In reference to ART alone, the IPT plus ART significantly reduced risks of active TB (adjusted odds ratio [AOR] 0.24; 95% CI 0.09–0.63; P=0.004) and had about 16 months of TB protection (P<0.001). In addition, the IPT plus ART delayed HIV progression to AIDS more significantly than the ART only (P=0.029). However, it increased risks of adverse events (AOR 3.33; 95% CI 1.35–8.19; P=0.01) more than the ART only. Conclusions: The wider use of IPT with ART impacts more on incidence of tuberculosis and time to AIDS while simultaneously increasing risks of adverse events than the ART only.