Evaluation of the time-dependent effects of factors influencing the hazard of disease recurrence in tuberculosis patients

Background & Aims: There are variables whose influence on the risk of tuberculosis (TB) recurrence change over time. Therefore, this study aimed to assess the time-dependent effects of these variables on the hazard of TB recurrence. Materials & Methods: In this historical cohort study, data were collected from 4,564 TB patients who were referred to the TB research center of Dr. Masih Daneshvari Hospital, Tehran, from 2005 to 2015, in order to evaluate factors affecting the hazard of TB recurrence in terms of time dependency or time constancy. Data were analyzed in STATA 14 software using a statistical test based on Schoenfeld residuals, the time-dependent effects method, and the time-varying effects model (considering time function as f (t) = t). Results: The results showed that only the impact of the variables of drug adverse effects and passive smoker were inconstant over time and had time-dependent effects, and they also influenced the hazard of TB recurrence. Also, the effect of the two mentioned variables on the hazard of TB recurrence displayed a decreasing and increasing trend with time, respectively. Conclusion: Using the time-varying effects model in the study of the hazard of TB recurrence allows evaluating the time-dependent effects of the studied variables and also can differentiate them from the time-independent variables.