June 2, 2022
Keio University School of Medicine
A research group led by the Division of Pulmonary Medicine, Department of Internal Medicine, Keio University School of Medicine, building on the achievements of the "COVID-19 Task Force," which includes Professor Koichi Fukunaga of the Division of Pulmonary Medicine and Professor Takanori Kanai of the Division of Gastroenterology and Hepatology, conducted a multi-center collaborative research study from November 2020 to the end of March 2022. The study targeted approximately 1,000 cases of patients aged 18 and older who were definitively diagnosed with and hospitalized for coronavirus disease (hereinafter, COVID-19) at 27 facilities nationwide between January 2020 and the end of February 2021.
In this study, we conducted a questionnaire survey using paper forms or a smartphone application to determine the presence or absence of 24 common symptoms after COVID-19 (post-COVID-19 conditions). The presence of each symptom was assessed during hospitalization and at 3, 6, and 12 months after diagnosis. We also investigated the impact on health-related QOL, tendencies toward anxiety and depression, fear of COVID-19, sleep disturbances, and labor productivity using various internationally recognized questionnaires.
The gender ratio of the analyzed cases was largely consistent with that of hospitalized COVID-19 cases in other previously reported studies, with a majority of patients being male. Furthermore, the cases were distributed across all age groups without significant bias.
The proportion of patients with at least one symptom showed a statistically significant decrease over time. However, it was confirmed that approximately one-third of patients still had at least one remaining symptom even 12 months after diagnosis. Furthermore, the analysis at the 3-month post-diagnosis mark revealed that the presence of even one post-COVID-19 condition was associated with impacts such as a decline in health-related QOL, increased tendencies toward anxiety and depression, heightened fear of COVID-19, worsened sleep disturbances, and reduced labor productivity.
This study is the largest survey to date on post-COVID-19 conditions in Japan and is the first report to examine these conditions over a long period, tracking symptoms observed up to discharge and then chronologically at 3, 6, and 12 months. Moreover, it is the first report of its kind in Japan in that it not only investigates the prevalence of each post-COVID-19 condition but also uses internationally established questionnaires, making the report multifaceted, highly quantitative, and easy to use for comparative analysis.
Moving forward, our research group will continue to conduct detailed analyses based on the collected data to clarify the actual situation of post-COVID-19 conditions in Japan. We aim to contribute not only to medical approaches for these conditions but also to public policy.
For the full press release, please see below.