ntroduction: Tuberculosis (TB) is one of the most prevalent infectious diseases in the world, causing major public health problems in developing countries. The rate of TB incidence in Iran was estimated to be 13 per 100,000 in 2021. This study aimed to estimate the reproduction number and serial interval for pulmonary tuberculosis in Iran. Material and Methods: The present national historical cohort study was conducted from March 2018 to March 2022 based on data from the National Tuberculosis and Leprosy Registration Center of Iran\\\\\\\'s Ministry of Health and Medical Education (MOHME). The study included 30,762 tuberculosis cases and 16,165 new smear- positive pulmonary tuberculosis patients in Iran. We estimated the reproduction number of pulmonary tuberculosis in a Bayesian framework, which can incorporate uncertainty in estimating it. Statistical analyses were accomplished in R software. Results: The mean age at diagnosis of patients was 52.3±21.2 years, and most patients were in the 35–63 age group (37.1%). Among the data, 9,121 (56.4%) cases were males, and 7,044 (43.6%) were females. Among patients, 7,459 (46.1%) had a delayed diagnosis between 1 and 3 months. Additionally, 3,039 (18.8%) cases were non-Iranians, and 2,978 (98%) were Afghans. The time-varying reproduction number for pulmonary tuberculosis disease was calculated at an average of 1.06±0.05 (95% Crl 0.96– 1.15). Conclusions: In this study, the incidence and the time-varying reproduction number of pulmonary tuberculosis showed the same pattern. The mean of the time-varying reproduction number indicated that each infected person is causing at least one new infection over time, and the chain of transmission is not being disrupted.

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