Case Characteristics, Resource Utilisation, and In-Hospital Mortality of 13,503 COVID-19 Patients Admitted to 566 Hospitals in Japan: An Observational Study

Abstract

Background: Studies of in-hospital mortality of COVID-19 patients among high-income countries with low infection rates with a nationwide database are scarce. We aimed to describe and gain comprehensive insight regard to in-hospital mortality, medical resource use of mechanical ventilators and ICU admission, and patient characteristics from COVID-19 patients in Japan. Method: This is a retrospective observational study using the nationwide insurance claims data of the DPC database in Japan. The study cohort included hospitalized patients aged 18 years or older with a diagnosis of COVID-19, based on patient data with completing hospital course from January 1, 2020 to September 30, 2020. Multivariate analysis using restricted cubic spline curves showed the relationships between in-hospital mortality and age, male sex, increased body mass index, decreased Barthel Index for activities of daily living, comorbidities based on Charlson comorbidity index and its score. Findings: During the study period, 13503 of the patients admitted for COVID-19 completed hospital course. The overall in-hospital mortality was 4·1%, and 3·0% (393 of 13005) in the non-ventilated group and 31·5% (157 of 498) in the ventilated group. The age-specific in-hospital mortality was higher in the older age, with in-hospital mortality of 31·0% in aged 80 years and more in the early pandemic period of March 2020, and declined to 14·9% even in the second pandemic in August 2020. 13005 patients (96·3%) completed their course without mechanical ventilation and 498 patients (3·7%) with mechanical ventilation. The overall median age was 50 years (IQR 33–68). The milder the COVID-19, the younger the median age tended to be: median 44 years (IQR 29–59) without any respiratory support, median 69 years (IQR 55–80) in the supplemental oxygen group, and median 69 years (IQR 58–78) in the ventilated group. In the multivariate analysis, an older age, male sex, increased body mass index, increased Charlson Comorbidity Index score and decreased Barthel Index were associated with the risk of in-hospital mortality. Interpretation: The in-hospital mortality rate for patients hospitalized with COVID-19 in Japan during the study period was considerably lower than that reported in previous studies using nationwide databases in other countries. This may reflect the low infection rate in Japan and the fact that the burden on medical resources did not exceed capacity. In the context of a pandemic, controlling the burden on medical resources is one of the important key factors for improving in-hospital mortality in patients with COVID-19. Funding Information: Ministry of Health, Labour and Welfare, Japan.Declaration of Interests: We declare no competing interests.Ethics Approval Statement: The study was conducted following the Ethical Guidelines for Medical Research Involving Human Subjects established by the Ministry of Health, Labour and Welfare, and was approved by the Ethics Committee of Tokyo Medical and Dental University (Research Ethics Committee No. M2000-788).