Impact of COVID-19 pandemic, and the mediating role of hospital caseload and severity on mortality of hospitalised tuberculosis patients in Thailand

Background The COVID-19 hospital caseload indicates the quality of hospital care, as resources were redirected to address the surge in COVID-19 cases. The study aimed to evaluate the impact of COVID-19 hospital caseload on hospital tuberculosis (TB) case fatality rate (CFR) mediated by the TB caseload and severity of patients. Methods A retrospective analysis of TB patients’ hospital admission data in Thailand extracted from the Thai Health Information Portal database between January 2017 and September 2022. Charlson Comorbidity Index (CCI) was used to determine the severity of hospitalised TB patients. An interrupted time series analysis, lag time analysis and serial mediation analysis were done. Results During COVID-19 pandemic, there was a 12.9% decrease in monthly hospital TB caseload, and a 14.1% increase in monthly TB hospital CFR compared to the counterfactual scenario had there been no COVID-19. COVID-19 hospital caseload had a strong negative correlation with TB hospital caseload (r = − 0.60, p -value = < 0.001), but a strong positive correlation with TB hospital CFR (r = 0.74, p -value = < 0.001) during the same month. An increase in average CCI score of 0.1 was associated with an increase of 2.3 deaths per 100 TB admissions. After adjusting the TB caseload and CCI of TB patients admitted to the hospital, no association was found between COVID-19 hospital caseload and the hospital CFR of TB patients. Conclusions The increase in TB hospital CFR during COVID-19 pandemic was likely driven by a higher proportion of severe cases being admitted, rather than a decline in hospitals’ quality of care.