Cost impact of culture reversion in extensively drug-resistant tuberculosis in Pakistan: a multi-center retrospective study.

Culture reversion among extensively drug-resistant tuberculosis (XDR-TB) patients leads to treatment prolongation and imposes a substantial economic burden on national tuberculosis programs; however, evidence quantifying this burden in high-burden countries such as Pakistan remains limited. This study aimed to quantify the additional treatment costs attributable to culture reversion and reconversion among XDR-TB patients managed under Pakistan's Programmatic Management of Drug-Resistant Tuberculosis (PMDT) program. This retrospective multicenter observational study used routinely collected data from 30 PMDT treatment centers across Pakistan. Culture-confirmed XDR-TB patients registered between May 2010 and June 2019 with complete clinical, microbiological, and treatment records were included. Culture conversion, reversion, and reconversion were defined according to World Health Organization criteria. Treatment costs were calculated using actual drug regimens received by patients and national procurement prices, adjusted to 2024 USD using official exchange rates and inflation indices. Additional costs were estimated for patients whose treatment duration exceeded the standard 24-month regimen due to reversion. Of 404 eligible XDR‑TB patients, 309 (76.5%) achieved initial culture conversion. Among these, 155 (38.3% of total; 50.2% of converters) experienced culture reversion, and 82 (20.3% of total) subsequently achieved reconversion. Forty‑six reconverted patients required treatment beyond 24 months. The cumulative additional drug cost attributable to reconversion‑related treatment prolongation was USD 28,295.54, fully borne by the national TB program. Culture reversion among XDR‑TB patients results in significant additional treatment costs for Pakistan's TB control program. Strengthening early treatment monitoring, adherence support, and individualized regimen optimization is essential to reduce reversion, limit unnecessary treatment extension, and mitigate economic burden.