[Study on transmission dynamic of 15 clusters of COVID-2019 cases in Ningbo].

To describe the basic characteristics of clusters of coronavirus diseases 2019 (COVID-19) cases in Ningbo, Zhejiang province, and evaluate the generation time (Tg) and basic reproduction number ((0)) of COVID-19. The basic information and onset times of the clusters of COVID-19 cases in Ningbo were investigated, the inter-generational interval of the cases were fitted by using gamma distribution, and the (0) was calculated based on the SEIR model. In the 15 clusters of COVID-19 cases, a total of 52 confirmed cases, 5 cases of nucleic acid-positive asymptomatic cases. The cases occurred from January 23 to February 4, the cases were mainly women. The incubation period was (6.11±3.38) days, and the median was 5 days. The Tg was (6.93±3.70) days. There were no significant differences in Tg between age group<60 years and age group 60 years and above, and between men and women (=0.551). According to the Tg calculated in this paper, the (0) of COVID-19 in Ningbo was 3.06 (95: 2.64- 3.51); according to the reported case transmission interval of 7.5 days in the literature, the (0) was 3.32 (95: 2.51-9.38). There is no age and gender specific differences in the Tg of clusters of COVID-19 cases in Ningbo, and COVID-19 has high infectivity and spreading power in early phase.