Paradoxical changes in tuberculosis diagnostic delay and bacteriological positivity across COVID-19 pandemic phases: a retrospective cohort study in Taiwan

Background The COVID-19 pandemic has substantially disrupted healthcare systems and may have influenced tuberculosis (TB) diagnosis through changes in healthcare access, diagnostic pathways, and respiratory disease surveillance. However, evidence remains limited regarding how these changes affected TB diagnostic intervals and case detection across different pandemic phases. Methods This retrospective cohort study included adult patients with newly diagnosed pulmonary TB at a medical center in southern Taiwan between 2017 and 2024. Patients were categorized into three periods: pre-pandemic, pandemic, and post-pandemic. Clinical characteristics, diagnostic intervals, and bacteriological positivity were compared across the three phases. Results A total of 789 patients were included (pre-pandemic: n = 341; pandemic: n = 270; post-pandemic: n = 178). Compared with the pre-pandemic period, both the pandemic (adjusted OR [aOR] 0.48, 95% CI 0.34–0.68, p < 0.001) and post-pandemic periods (aOR 0.36, 95% CI 0.24–0.53, p < 0.001) were independently associated with reduced odds of diagnostic delay. Conversely, the post-pandemic period was independently associated with higher odds of smear positivity (aOR 1.92, 95% CI 1.28–2.87, p = 0.002), without a corresponding increase in cavitary lesion prevalence. Incidental diagnosis was independently associated with increased diagnostic delay (aOR 2.14, 95% CI 1.40–3.28, p < 0.001). Conclusions The COVID-19 pandemic was associated with a paradoxical pattern in pulmonary TB detection with progressive improvement in diagnostic efficiency alongside a post-pandemic shift toward higher bacteriological positivity, consistent with a pandemic-driven case-mix change rather than a uniform increase in disease severity. Sustaining expanded diagnostic capacity and ensuring equitable healthcare access remain critical priorities for TB control during public health emergencies.