A problem of self-isolation in Japan: The relationship between self-isolation and COVID-19 community case

Background: The Japanese government advised mild or asymptomatic coronavirus disease-2019 (COVID-19) cases to self-isolate at home, while more severe individuals were treated at health posts. Poor compliance with self-isolation could be a potential reason for the new outbreak. Our study aimed to find out the correlation between the rising new cases of COVID-19 and home-based patients in Japan. Methods: A secondary data analysis study was conducted with the data from COVID-19- involved databases collected from Johns Hopkins University, Japanese Ministry of Health, Labour and Welfare, and Community Mobility Reports of Google. New community cases, stringency index, number of tests, and active cases were analyzed. Using a linear regression model, an independent variable was utilized for a given date to predict the future number of community cases. Results: Research results show that outpatient cases, the stringency, and Google Mobility Trend were all significantly associated with the number of COVID-19 community cases from the sixth day to the ninth day. The model predicting community cases on the eighth day (R2=0.8906) was the most appropriate showing outpatients, residential index, grocery and pharmacy index, retail and recreation index, and workplaces index were positively related (β₁=24.2, 95% CI: 20.3- 26.3, P<0.0001; β₂=277.7, 95% CI: 171.8-408.2, P<0.0001; β₃=112.4, 95% CI: 79.8-158.3, P<0.0001; β₄=73.1, 95% CI: 53- 04.4, P<0.0001; β₅=57.2, 95% CI: 25.2-96.8, P=0.001, respectively). In contrast, inpatients, park index, and adjusted stringency index were negatively related to the number of community cases (β₆=-2.8, 95% CI: -3.9 - -1.6, P<0.0001; β₇=-33, 95% CI: -43.6 - -27, P<0.0001; β₈=-14.4, 95% CI: -20.1- -12, P<0.0001, respectively). Conclusion: Outpatient cases and indexes of Community Mobility Reports were associated with COVID-19 community cases.