Yoneoka, DaisukeKawashima, TakayukiTanoue, YutaNomura, ShuheiEjima, KeisukeShi, ShoiEguchi, AkifumiTaniguchi, ToshibumiSakamoto, HarukaKunishima, HiroyukiGilmour, StuartNishiura, HiroshiMiyata, Hiroaki2020-07-022020-07-022020-05-30Yoneoka, D., Kawashima, T., Tanoue, Y., Nomura, S., Ejima, K., Shi, S., Eguchi, A., Taniguchi, T., Sakamoto, H., Kunishima, H., Gilmour, S., Nishiura, H., & Miyata, H. (2020). Early SNS-based monitoring system for the COVID-19 outbreak in Japan: A population-level observational study. Journal of Epidemiology. https://doi.org/10.2188/jea.JE20200150https://hdl.handle.net/1805/23154Background: The World Health Organization declared the novel coronavirus outbreak (COVID-19) to be a pandemic on March 11, 2020. Large-scale monitoring for capturing the current epidemiological situation of COVID-19 in Japan would improve preparation for and prevention of a massive outbreak. Methods: A chatbot-based healthcare system named COOPERA (COvid-19: Operation for Personalized Empowerment to Render smart prevention And care seeking) was developed using the LINE app to evaluate the current Japanese epidemiological situation. LINE users could participate in the system either though a QR code page in the prefecture’s website, or a banner at the top of the LINE app screen. COOPERA asked participants questions regarding personal information, preventive actions, and non-specific symptoms related to COVID-19 and their duration. We calculated daily cross correlation functions between the reported number of infected cases confirmed by PCR and the symptom-positive group captured by COOPERA. Results: We analyzed 206,218 participants from three prefectures reported between March 5 and 30, 2020. The mean (standard deviation) age of participants was 44.2 (13.2). No symptoms were reported by 96.93% of participants, but there was a significantly positive correlation between the reported number of COVID-19 cases and self-reported fevers, suggesting that massive monitoring of fever might help to estimate the scale of the COVID-19 epidemic in real time. Conclusions: COOPERA is the first real-time system being used to monitor trends in COVID-19 in Japan, and provides useful insights to assist political decisions to tackle the epidemic.en-USAttribution 4.0 InternationalCOVID-19JapanLarge-scale Monitoring SystemArticle