Estimation of incubation period distribution of COVID-19 using disease onset forward time: a novel cross-sectional and forward follow-up study

Qin Jing; Chong You; Qiushi Lin; Taojun Hu; Shicheng Yu; Xiao-Hua Zhou

is the (which was not peer-reviewed) The copyright holder for this preprint . https://doi.org/10.1101/2020.03.06.20032417 doi: medRxiv preprint Wuhan. However, starting January 19, the China CDC began issuing test reagents to all provinces, confirmed cases were reported outside Hubei province in mainland China, the severity of COVID-19 was widely noted by the public, and various strict containment measures were implemented to minimize human-to-human transmission. 2 Thus, it is unlikely that confirmed cases who left Wuhan after January 19, 2020, were infected outside Wuhan and assumption (A5) is supported. To ensure that the follow-up time is long enough such that no additional biased sampling occurred in this study, we excluded all cases who left Wuhan after January 23, 2020, which leaves an average follow-up time of 25 days (from date of departure to February 15, which is the end of this study). A 25-day follow-up period should be long enough based on the various studies on the incubation period of COVID-19. [3] [4] [5] [6] Note that those who left Wuhan after January 23 might not have enough time to develop symptoms before the end of the followup period. Including these cases in the cohort might lead to a downward bias on the incubation period.