Short-term risk of pulmonary tuberculosis after influenza in adults: a population-based self-controlled case series study

Objectives Influenza infection may impair host immune control of Mycobacterium tuberculosis , but the short-term risk of active pulmonary tuberculosis (PTB) following influenza in adults remains unclear. We aimed to quantify this risk and identify the specific time window of elevated risk. Methods We conducted a population-based self-controlled case series study using surveillance data from Chaoyang District, Beijing, 2016–2025. Individuals aged ≥15 years with both influenza infection and a first episode of active PTB were included. Conditional Poisson regression was used to estimate incidence rate ratios (IRRs) for PTB during predefined post-influenza risk windows (days 1–30, 31–60, and 61–90 after influenza onset), and a pre-exposure negative-control window (days −30 to −1), compared with baseline periods, adjusting for age and calendar time season. Results A total of 540 individuals were included. The IRR for PTB during the pre-exposure window was 3.36 (95% CI: 1.92–5.88). The risk was highest in the first 30 days (IRR: 6.68, 95% CI: 4.48–9.94), rapidly declined to 3.61 (95% CI: 2.10–6.19), during days 31–60, and returned to baseline by days 61–90 (IRR: 1.05, 95% CI: 0.39–2.82). The association effect in the first 30 days was markedly stronger in older adults (IRR: 13.06) and those with bacteriologically positive tuberculosis (IRR: 9.98). Sensitivity analyses supported these findings. Conclusion Influenza infection was associated with a transient increase in the risk of PTB, concentrated in the first 30 days and rapidly declining thereafter, returning to baseline by 90 days, with a stronger association among older adults. Influenza may act as a short-term trigger for PTB progression or reactivation. Enhanced PTB vigilance after influenza and influenza vaccination may offer public health benefits.