Epidemiological Characteristics and Incubation Period of 7015 Confirmed Cases With Coronavirus Disease 2019 Outside Hubei Province in China

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 23 January 2020. Methods. Information on 7015 confirmed cases from 19 January to 8 February 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. The median incubation period was 5 days and extended from 2 days on 23 January to 15 days on 8 February. The proportion of imported cases decreased from 85.71% to 33.19% after 23 January. In addition, lengths of intervals between onset and diagnosis, onset and first visit, and first visit and diagnosis decreased over time. Conclusions. Rapidly transmitting COVID-19 has a short incubation period. The onset mainly occurred among young to middle-aged adults. Traffic restrictions played an important role in the decreased number of imported cases outside Hubei.