Impact of COVID-19 pandemic on pneumonia trends in Japan: Insights from diagnosis procedure combination data

This study analyzed changes in pneumonia hospitalizations in Japan before and after the COVID-19 pandemic using Diagnosis Procedure Combination data. The proportion of inpatients with non-aspiration pneumonia (non-AP) decreased by 48.8%, whereas that of inpatients with aspiration pneumonia (AP) decreased by only 8.8%. The proportion of AP among all pneumonia cases increased from approximately 33%–47% post-pandemic. The significant reduction in non-AP incidence likely reflects its sensitivity to external factors such as public health measures. Conversely, the limited decrease in AP demonstrates its stronger association with internal factors that are less affected by lifestyle changes. This study provides insights into the differential impact of the pandemic on pneumonia subtypes, revealing how external interventions may have varying effects on different forms of pneumonia. These findings highlight the complex interplay between public health measures and the epidemiology of respiratory infections in the context of a global pandemic.