Factors associated with time to sputum culture conversion among pulmonary tuberculosis patients in Nairobi, Kenya: A prospective cohort study

Abstract

Tuberculosis (TB) control in high-burden sub-Saharan African settings remains challenging. Sputum culture conversion remains a key indicator of treatment response and reduced infectiousness. This study identified predictors of time to sputum culture conversion among pulmonary TB patients in Nairobi, Kenya, to inform localized context to-specific interventions. From 328 newly diagnosed patients with pulmonary TB at a public chest clinic (2022-2023), 100 with microbiological confirmation of either GeneXpert or smear microscopy were systematically selected for this prospective cohort study. The primary endpoint, time to sputum culture conversion, was assessed weekly with Mycobacteria Growth Indicator Tube (MGIT) cultures. Predictors of conversion were identified using Cox proportional hazards regression, adjusted for clinical and demographic factors. By the end of intensive phase (week8), approximately 60% of patients had their sputa converted to culture negative with only one participant sputa converting beyond 20 weeks. Smoking (adjusted hazard ratio [aHR]=1.74, 95% CI: 1.0-3.04; p=0.05) and phenotypic resistance to first-line TB drugs (aHR=2.51, 95% CI: 1.06-5.94; p=0.04) were independently associated with delayed sputum culture conversion. Conversely, patients with scanty baseline microbial loads (Ziehl-Neelsen [ZN] grade) had accelerated conversion compared to those with high loads (ZN 2+/3+; aHR=1.78, 95% CI: 1.01-3.13; p=0.047). Body mass index and Human Immuno-deficiency Virus (HIV) status showed no significant association (p>0.05). High baseline microbial load, phenotypic drug resistance, and smoking substantially prolonged patients’ conversion to culture negative status. These findings underscore the importance of tailored strategies of addressing local determinants essential to optimize TB control in sub-Saharan Africa. Intensified monitoring of high-bacterial-load patients, early drug susceptibility testing, and the urgency of integrating smoking cessation programs, in high-burden settings, are crucial for improving treatment outcomes and controlling transmission of tuberculosis.