Descriptive epidemiology of COVID-19 in Japan 2020: insights from a multihospital database

Epidemiological data are essential for developing strategies against the current coronavirus disease 2019 (COVID-19) pandemic. Data on COVID-19 epidemiology in Japan are limited owing to a focus on specific regions and patient groups, particularly in the early phase of the pandemic.

We investigated COVID-19 epidemiology in Japan in 2020 using a large nationwide multihospital database containing insurance claim records and medical records. Inclusion criteria were inpatient and outpatient referrals for COVID-19 in 2020. We analyzed demographic data, comorbidities, drug use, severe COVID-19 risk, and clinical course of hospitalized patients (including death).

We identified 11,868 COVID-19 cases from 56 institutions: 6,440 outpatients and 5,428 inpatients. Of the patients, 53.2% had comorbid conditions, the most common of which was tumor (22.1%), and 56.4% were classed as having a high risk of COVID-19. Pharmacological management patterns were generally consistent between the first and second half of 2020, except for glucocorticoid use. The use of unauthorized medications (hydroxychloroquine, ivermectin, and favipiravir) was infrequent. For hospitalized patients, the median length of stay was 10 days, and 2.4% of patients were admitted to intensive care units. Post-COVID-19 all-cause mortality, all-cause 30-day mortality, and in-hospital deaths were recorded for 7.9%, 5.4%, and 4.6% of patients, respectively. Patients with high-risk conditions had a lower survival probability.

This descriptive study of COVID-19 in 2020 identified differences in care across outpatient and inpatient settings and changes in care delivery as the pandemic progressed. These findings could inform strategies for future infectious disease pandemics.