Time to and factors associated with incident tuberculosis among PLHIV on ART and isoniazid preventive therapy in selected Kampala public health facilities

Abstract

Introduction: People Living with HIV (PLHIV) are treated with Isoniazid to lower the risk of incident Tuberculosis disease. In Uganda, routine HIV program data in DHIS2, showed a rising trend of new TB cases in this population. The duration of IPT, protectiveness and factors associated with incident TB are unknown. This study aimed to determine the TB incident rate, time to incident TB and factors associated with incident TB. Methods: The study was a retrospective cohort, using program data from electronic medical records. Systematic sampling was used to select 6136 PLHIV on ART, who started IPT after 1st January 2019, observed for 4 years until December 2022 in three selected public health facilities. Data was analyzed using STATA version .15.0. TB incidence rate was computed as number of new TB cases divided by the total person months of observation. The time to incident TB was determined by dividing the total sum of event and censored time by the total number of subjects observed. The factors associated with incident TB were determined by Cox regression analysis. Results: Out of the 6136 participants, majority (71%, n = 4380) were female. Only 2% (n=107) were 14 years and below and 99.5% (n = 5460) were in WHO clinical stage 1 or 2. The TB incidence rate was 22.85/100,000 person months [95% CI (16.25/100,000, 31.24/100,000)]. The average survival time to incident TB was 27.8 months (SD 10.8) and factors associated with incident TB included having a higher WHO clinical stage 3 or 4 [aHR = 164.73, 95% CI (50.86, 533.59)] and categories of ART regimen with Efavirenz [aHR = 0.11, 95% CI (0.03, 0.36)] or Nevirapine [aHR = 0.09, 95% CI (0.01, 0.89)]. Baseline CD4 and years on ART remained in the model because they confounded the relationship between WHO clinical stage and regimen with incident TB respectively. Similarly, non-suppressed viral load and sex confounded the relationship between regimen and incident TB. Conclusions: The TB incidence rate among people living with HIV on ART who started IPT was low at 22.85 per 100,000 person months. The average survival time to incident TB was 27.8 months occurring between 1.5 and 3.1 years. To protect PLHIV on ART from incident TB disease, there is need to repeat IPT among PLHIV on ART who were previously treated with IPT 27.8 months ago especially those of WHO clinical stage 3 or 4