Incubation Period and Other Epidemiological Characteristics of 2019 Novel Coronavirus Infections with Right Truncation: A Statistical Analysis of Publicly Available Case Data

Abstract

The geographic spread of 2019 novel coronavirus (COVID-19) infections from the epicenter of Wuhan, China, has provided an opportunity to study the natural history of the recently emerged virus. Using publicly available event-date data from the ongoing epidemic, the present study investigated the incubation period and other time intervals that govern the epidemiological dynamics of COVID-19 infections. Our results show that the incubation period falls within the range of 2-14 days with 95% confidence and has a mean of around 5 days when approximated using the best-fit lognormal distribution. The mean time from illness onset to hospital admission (for treatment and/or isolation) was estimated at 3-4 days without truncation and at 5-9 days when right truncated. Based on the 95th percentile estimate of the incubation period, we recommend that the length of quarantine should be at least 14 days. The median time delay of 13 days from illness onset to death (17 days with right truncation) should be considered when estimating the COVID-19 case fatality risk.

Keywords: distribution; emerging infectious diseases; epidemiology; incubation period; virus.

Figure 1

Probability distributions of the time from illness onset or hospital admission to hospital admission or death for COVID-19 outbreak cases reported through 31 January 2020. (A) Probability density of the time from illness onset to hospital admission in days set to the best-fit gamma distribution. (B) Probability density of the time from illness onset to death in days set to the best-fit lognormal distribution. (C) Probability density of the time from hospital admission to death in days set to the best-fit Weibull distribution.

Figure 2

Estimated cumulative distribution for the incubation period of COVID-19 infections from outbreak cases reported through 31 January 2020. The data are from public case reports. Left and center: non-truncated estimates excluding (n = 52) and including (n = 158) Wuhan residents. Right: right-truncated estimates excluding Wuhan residents (n = 52).