Trends in COVID-19 Outbreak in Tokyo and Osaka from January 25 to May 6, 2020: a Joinpoint Regression Analysis of the Outbreak Data

We analyzed the trends of the coronavirus disease 2019 (COVID-19) outbreak in Tokyo and Osaka from January 25 to May 6, 2020. To analyze the trends and identify significant changes in them, we performed a joinpoint regression analysis. From the last week of March, the number of COVID-19 cases soared in Tokyo (β = 103.51) and Osaka (β = 28.07). During the 2nd and 3rd weeks of April, both Tokyo (β = 157.53) and Osaka (β = 60.96) experienced peak growth in COVID-19 cases. Since almost 14 days after the state of emergency declaration, the number of cases showed a containment trend in Osaka, but continued to increase at a concerning rate in Tokyo (β = 90.66).