Prevalence, risk factors and treatment outcomes of isoniazid resistant TB in Bulawayo city, Zimbabwe: A cohort study

Introduction: The isoniazid-resistant TB poses a threat to TB control efforts. Zimbabwe, one of the high TB burden countries, has not explored the burden of isoniazid resistant TB. Hence among all bacteriologically-confirmed TB patients diagnosed in Bulawayo City during March 2017 and December 2018, we aimed to assess the proportion with isoniazid resistant TB and associated factors. Also, we aimed to describe the TB treatment outcomes. Methodology: A cohort study involving routinely collected data by the National TB Reference Laboratory (NTBRL) in Bulawayo City and National TB programme of Zimbabwe. The percentage with 95% confidence interval (CI) was used to express the proportion with isoniazid-resistant TB. The modified Poisson regression was used to assess the association of demographic and clinical characteristics with isoniazid mono-resistant TB. Results: Of 2160 bacteriologically-confirmed TB patients, 1612 (74.6%) had their sputum received at the NTBRL and 743 (46.1%) had culture growth. Among those with culture growth, 34 (4.6%, 95% CI: 3.5-6.7) had isoniazid mono-resistant TB, 25 (3.3%, 95% CI: 2.2-4.9) had MDR-TB. Thus, 59 (7.9%, 95% CI: 6.1-10.1) had isoniazid-resistant TB. Children < 15 years had a higher prevalence of isoniazid mono-resistant TB (aPR= 3.93; 95% CI: 1.24-12.45). Among those with rifampicin sensitive TB, patients with isoniazid-sensitive TB had higher favourable treatment outcomes compared to those with isoniazid-resistant TB (86.3% versus 75.5%, p = 0.039). Conclusions: The prevalence of isoniazid-resistant TB was low compared to neighbouring countries with high burden of TB-HIV. However, Zimbabwe should consider reviewing treatment guidelines for isoniazid mono-resistant TB due to the observed poor treatment outcomes.