Validity of Time to Sputum Culture Conversion to Predict Cure in Patients with Multidrug-Resistant Tuberculosis: A Retrospective Single-Center Study

To evaluate the predictive value of time to sputum culture conversion (SCC) in predicting cure and factors associated with time to SCC and cure in multidrug-resistant tuberculosis (MDR-TB) patients, a retrospective study was conducted at programmatic management unit of drug resistant tuberculosis (TB), Peshawar. A total of 428 pulmonary MDR-TB patients enrolled at the study site from January 1, 2012 to August 31, 2014 were followed until treatment outcome was recorded. Survival analysis using Cox proportional hazards model and multivariate binary logistic regression were, respectively, used to identify factors associated with time to SCC and cure. A P value < 0.05 was considered statistically significant. Overall, 90.9% patients achieved SCC, and 76.9% were cured. Previous use of second-line drugs (SLDs) (hazard ratio [HR] = 0.637; 95% confidence interval [CI] = 0.429-0.947), ofloxacin resistance (HR = 0.656; 95% CI = 0.522-0.825) and lung cavitation (HR = 0.744; 95% CI = 0.595-0.931) were significantly associated with time to SCC. In predicting cure, sensitivities of SCC at 2, 4, and 6 months were 64.1% (95% CI = 58.69-69.32), 93.0% (95% CI = 89.69-95.52), and 97.6% (95% CI = 95.27-98.94), respectively, whereas specificities were 67.7% (95% CI = 57.53-76.73), 51.5% (95% CI = 41.25-61.68), and 44.4% (95% CI = 34.45-54.78), respectively. Furthermore, patients' age of 41-60 (odds ratio [OR] = 0.202; 95% CI = 0.067-0.605) and > 60 years (OR = 0.051; 95% CI = 0.011-0.224), body weight > 40 kg (OR = 2.950; 95% CI = 1.462-5.952), previous SLD use (OR = 0.277; 95% CI = 0.097-0.789), lung cavitation (OR = 0.196; 95% CI = 0.103-0.371) and ofloxacin resistance (OR = 0.386; 95% CI = 0.198-0.749) were significantly associated with cure. Association of SCC with cure was substantially stronger at 6 months (OR = 32.10; 95% CI = 14.34-71.85) than at 4 months (OR = 14.13; 95% CI = 7.92-25.21). However in predicting treatment outcomes, the combined sensitivity and specificity of SCC at 4 months was comparable to SCC at 6 months. Patients with risk factors for delayed SCC were also at high risk of unsuccessful outcomes.