LAUSR

Objective: To investigate the epidemiological characteristics of COVID-19 caused by 2019-nCoV Delta variant in Shangyu district, Shaoxing of Zhejiang province in 2021, and provide evidence for the improvement of COVID-19 control and prevention measures. Methods: The incidence data of COVID-19 in Shangyu from December 7 to 21, 2021 was obtained from Shangyu District Center for Disease Control and Prevention. The epidemiological characteristics of the cases, i.e. the population, time and space distributions, were analyzed, and the incubation period and time-varying reproduction numbers (Rt) were calculated. Results: From December 7 to 21, 2021, a total of 380 COVID-19 cases caused by 2019-nCoV Delta variant were detected in Shangyu, the median age of the cases was 52 years, M (Q1，Q3: 38, 61). The male to female ratio of the cases was 1∶1.25, and the cases were mainly workers (36.58%) and farmers (27.63%). The epidemic affected 9 townships (or community) of Shangyu, especially Caoe and Baiguan communities with the cases accounting for 57.10% and 31.53% respectively. The median incubation period of cases was 4.00 days, M (Q1，Q3: 3.00, 5.75). The basic reproduction number (R0) was 4.06, and the Rt was 5.62 in early phase of the outbreak (the highest) and continuously decreased to less than 1.00 within 10 days after the detection of the outbreak. The number of COVID-19 cases decreased to 0 within 14 days after the outbreak (December 7-21), and the main detection methods were screening in centralized isolation (55.53%) and home isolation (40.00%). The infection rates of close contacts and secondary close contacts were 2.06% and 0.46% respectively. Conclusion: The epidemic of COVID-19 in Shangyu characterized by short incubation period, large number of infected people, and case clustering, suggesting the strong transmission of Delta variant (B.1.617.2). Comprehensive prevention and control measures, such as management of close contacts and secondary close contacts, and high-risk area, are essential for the rapid control of the epidemic.