Tuberculosis prevalence in individuals with past TB: Findings from a subnational TB prevalence survey from South India

Background: Previously treated tuberculosis (TB) contributes significantly to the TB burden. We examined the prevalence and characteristics of previously treated TB using data collected as part of a subnational TB prevalence survey in South India. Methods: A population-based pulmonary TB prevalence survey was conducted from 2021 to 2022 among individuals aged >15 years across districts of Tamil Nadu. Among individuals with a history of previous TB treatment, those diagnosed with microbiologically confirmed pulmonary TB during the survey were classified as previously treated TB. Crude and adjusted prevalence of previously treated TB was calculated. Results: Of the 130,914 individuals analyzed, 1,750 (1.34%) had history of previous TB treatment. The adjusted TB prevalence among individuals with a history of previous TB treatment versus those without was 2,238 vs. 207 per 100,000. The adjusted TB prevalence of previously treated TB was higher in males; individuals aged >45 years; those with low BMI (<18.5 kg/m²), diabetes, smoking, and alcohol use. The number needed to screen to identify one case of TB based on crude TB prevalence in the general population was 537, compared to 50 among individuals with a history of previous TB treatment. Conclusion: There is a high burden of TB in individuals with a history of previous TB treatment, emphasizing the importance of post-treatment monitoring and targeted interventions to address vulnerabilities.