Epidemiological characteristics and incubation period of 7,015 confirmed cases with Coronavirus Disease 2019 outside Hubei Province in China

Nie, Xiuquan; Fan, Lieyang; Mu, Ge; Tan, Qiyou; Wang, Mengyi; Xie, Yujia; Cao, Limin; Zhou, Min; Zhang, Zhuang; Chen, Weihong

BACKGROUND: Disease caused by SARS-CoV-2 broke out in Wuhan in December 2019. We utilized confirmed cases outside Hubei Province to analyze epidemiologic characteristics and evaluate the effect of traffic restrictions implemented in Hubei beginning on January 23, 2020. METHOD: Information on 7,015 confirmed cases from January 19 to February 8, 2020, in all provinces outside Hubei was collected from the national and local health commissions in China. Incubation period and interval times were calculated using dates of the following events: contact with an infected person, onset, first visit and diagnosis. We evaluated changes in incubation period and interval times. RESULTS: The average age of all cases was 44.24 years old. The median incubation period was 5 days and extended from 2 days on January 23 to 15 days on February 8. The proportion of imported cases decreased from 85.71% to 33.19% after January 23. In addition, the lengths of the intervals between onset and diagnosis, onset and first visit, and first visit and diagnosis decreased over time. CONCLUSION: Rapidly transmitting COVID-19 has a short incubation period. The onset mainly occurs among young to middle-aged adults. Traffic restrictions played an important role in the decreased number of imported cases outside Hubei.