Study population and setting
The study population included 181 persons with confirmed SARS-CoV-2 infection outside Hubei province, China between January 4, 2020, and February 24, 2020. Data were collected from news reports and press releases from areas without known community transmission including 50 provinces, regions, and countries outside Wuhan, Hubei province, China. Data included demographic characteristics and dates and times of possible exposure, symptom onset, fever onset, and hospitalization.
Summary of Main Findings
The median incubation period was estimated to be 5.1 days (95% CI, 4.5 to 5.8 days) and 97.5% of those who develop symptoms will do so within 11.5 days (CI, 8.2 to 15.6 days) of infection. The authors estimate that 101 out of every 10 000 cases will develop symptoms after 14 days of active monitoring or quarantine. The median time from symptom onset to hospitalization was estimated to be 1.2 days with a range of 0.2 to 29.9 days.
The methodological approach of this analysis to estimate the median incubation period, leveraging data across settings, is a strength of this study. Additionally, sensitivity analyses were conducted to account for possible bias from symptoms of cough or sore throat of other etiology, assumptions about the occurrence of local transmission, and to test other commonly used parameterizations.
As described in this study, publicly reported cases used in this study may overrepresent severe cases and underrepresent mild cases. Therefore, the incubation period estimated in this study may differ for mild cases.
Incubation period is an important measure for understanding the natural history of disease in the novel coronavirus and to inform epidemic response efforts.