Epidemiological investigation of a coronavirus disease 2019 epidemic and emergency response in Shanghai

Objective To analyze the epidemiological investigation results and emergency response to a coronavirus disease 2019 （COVID-19） epidemic in Shanghai.

Methods Descriptive epidemiological method was used to describe the epidemiological characteristics， such as population， time and spatial distribution of a COVID-19 epidemic on January 20， 2021 in Huangpu District of Shanghai. The advantages and disadvantages of the emergency response to this epidemic were analyzed.

Results All of the 22 cases were found by active screening， which included high-risk population screening （18.2%， 4/22）， medium-risk area screening （9.1%， 2/22）， and close contact population screening （72.7%，16/22）. The first 2 cases were detected by routine nucleic acid screening for staff in two hospitals. The confirmed cases appeared mostly during the first 3 days of the epidemic （45.5%，10/22）， and mainly distributed in the neighborhood C of Huangpu district. There were 6 key locations or regions of Huangpu District involved in this epidemic， and different control measures were adopted in these different regions according to the risk assessments. After precise epidemic prevention and control， it took only 14 days from the first to the last confirmed case of this epidemic （from January 21， 2021 to February 4， 2021）， and no new related cases appeared afterwards.

Conclusion Active screening and early finding of COVID-19 cases play a key role in timely control of the epidemic， with the smallest cost， the highest efficiency and the most limited urban impact.