Effectiveness of isoniazid preventive treatment among patients on antiretroviral treatment in Southeast Nigeria: A retrospective cohort study

Abstract

Introduction: Isoniazid preventive treatment has been shown to reduce the risk of developing tuberculosis (TB) among HIV patients. It is, however, not clear if receiving a 6-month course of isoniazid preventive treatment (IPT) confers additional protection among HIV patients already on ART. We compared the incidence of TB among adult HIV patients on ART who had received IPT for 6 months with those who had not received IPT and identified factors associated with the development of TB to in our operational context. Methods: We conducted a retrospective cohort study on adult HIV patients who commenced ART from January 2010 to December 2016. Patients who had a 6-months course of IPT were classified as exposed, while patients who had not received IPT or had not received the complete IPT for six months were classified as unexposed. The outcome measure was the development of TB. We included 324 exposed and 337 unexposed patients’ records. We followed them up for a total of 1338.6-person-years of observation with a median follow-up period of 19.8 months. We used a data extraction form to collect data from the patient case notes. Incidence density of developing TB in person-years, incidence rate ratio, Kaplan Meier survival function, and Cox proportionate regression model at 5% significance level were computed. The log-rank ratio was used to compare the equality of the survival function. Results: Six hundred and sixty-one patients were recruited for the study with a mean age of 38.5±9.6 years. The incidence of TB among the exposed was 10.6 cases per 1000-person-years of observation and among the unexposed was 16.6 cases per 1000-person-years of observation (incidence rate ratio=0.64, 95%CI: 0.15-1.97). WHO clinical stage 3 and 4 (adjusted hazard ratio [aHR]:4.8, 95% Confidence interval [95%CI]: 1.78-12.94) and poor ART adherence (aHR:3.5, 95%CI: 1.11-11.24) increased risk of development of the TB among the participants. There was no difference in the Kaplan-Meier survival functions between the exposed and unexposed (log-rank test χ2 =1.58, p=0.209). Conclusion: HIV patients on ART who had received a 6-months course of IPT have a lower risk of developing TB compared to those who have not though not statistically significant. Development of TB was also predicted by being in WHO clinical stage 3 and 4 at baseline and having poor adherence to ART. The risk of developing TB remains high among patients on ART. There is a need to consider reviewing isoniazid treatment for patients on AR