Hospitalization of mild cases of community-acquired pneumonia decreased more than severe ones during the COVID-19 epidemic

Objective The epidemic of the coronavirus disease 2019 (COVID-19) has affected the entire health care systems. Our aim was to assess the impact of the COVID-19 epidemic on the number and severity of cases for community-acquired pneumonia (CAP) in Japan. Methods Using claims data from the Quality Indicator/Improvement Project (QIP) database, we included urgent cases of inpatients for CAP from August 1, 2018, to July 30, 2020. We compared the monthly ratio of inpatient cases from August 2018 to July 2019 and August 2019 to July 2020 as a year-over-year comparison. We also compared this ratio according to the severity score “A-DROP” and performed an interrupted time series analysis (ITS) to evaluate the impact of the COVID-19 epidemic on the monthly number of inpatient cases. Results A total of 67,900 inpatient cases for CAP in 262 hospitals were included. During the COVID-19 epidemic (defined as the period between March and July 2020), the number of inpatient cases for CAP drastically decreased during the epidemic compared with the same period in the past year (−48.1%), despite only a temporary reduction in the number of other urgent admissions. The number of inpatient cases decreased according to the severity of pneumonia. Milder cases showed a greater decrease in the year-over-year ratio than severe ones (mild −55.2%, moderate −45.8%, severe −39.4%, and extremely severe − 33.2%). The ITS analysis showed that the COVID-19 epidemic reduced the monthly number of inpatient cases for CAP significantly (estimated decrease: −1233 cases; 95% CI, −521 to −1955). Conclusions Our study showed a significant reduction in the number of inpatient cases for CAP during the COVID-19 epidemic in Japan. The milder cases showed a greater decrease in the year-over-year ratio of the number of inpatient cases.