Résumé
Objective An epidemic of COVID-19 caused by an imported Delta variant strain in Guangzhou was investigated, and the transmission chain, transmission characteristics and infection of each case were analyzed, so as to provide a theoretical basis for predicting disease development and epidemic prevention and control. Methods By collecting the information released by Guangzhou government, the confirmed cases with a clear transmission chain were selected, and the infectious disease indicators such as serial interval (SI), basic reproduction number (Rq) and time-dependent reproduction number (Rt) were calculated to analyze the epidemiological characteristics. Results From May 21 to June 20, 2021, a total of 144 cases of indigenous COVID-19 were confirmed in Guangzhou, among which 67 pairs of cases with a clear transmission chain were selected. SI was calculated to follow the Gamma distribution, with a mean of 4. 27 d and a standard deviation of 2.65 d. Rq = 3. 18 (95% CI: 2. 1974.428), and Rt showed an obvious decreasing trend over time. On June 10, Rt = 0.97 (95% CI: 0. 751 -1. 214), which was lower than 1. Since then Rt had been less than 1, and it got smaller and smaller over time. Conclusion In this COVID-19 epidemic, the SI was shorter and the Rq was larger, which indicated that the Delta variant strain had a faster transmission rate and stronger transmissibility than the COVID-19 infected in Wuhan in 2020.