COVID-19 incubation period

COVID-19 Incubation Period: An Update

Stephen G. Baum, MD reviewing Lauer SA et al. Ann Intern Med 2020 Mar 10

Median and maximum incubation periods are estimated from patients connected to the disease-origin province in China.

Infection with SARS-CoV-2, the virus that causes COVID-19, appears to be highly contagious and is primarily spread by droplets. Containment efforts have emphasized quarantine during the incubation period as the most effective measure to limit spread. Because of the personal and economic toll of this measure and its implication for transmission, we need to maximize our understanding of the incubation period. These authors studied the case records of 181 patients (median age, 44.5 years; 60% male) who had visited Wuhan, the city in China where the infection was first identified (161 cases), or been in contact with an infected person before becoming symptomatic and testing positive for COVID-19 between January 4 and February 24, 2020. The investigators classified risk for undetected symptomatic infection as low (1 in 10,000), medium (1 in 1000), or high (1 in 100) and considered monitoring programs of varying length.

In the resulting models, estimated median incubation time (IT) of COVID-19 was 5.1 days; mean IT was 5.5 days. For 97.5% of infected persons, symptoms appear by 11.5 days. Fewer than 2.5% are symptomatic within 2.2 days. Estimated median IT to fever was 5.7 days. Among 108 patients diagnosed outside mainland China, median IT was 5.5 days; the 73 patients diagnosed inside China had a median IT of 4.8 days. Using exposures designated as high risk and a 7-day monitoring period, the estimate for missed cases was 21.2 per 10,000. After 14 days, the estimated number of missed high-risk cases was 1 per 10,000 patients.

COMMENT

These findings confirm the current recommendations for quarantine: Most patients who become symptomatic do so within 11 or 12 days and the vast majority within 14 days. However, we already know that asymptomatic or mildly symptomatic persons can transmit infection, and this group was not included here. Better access to testing for asymptomatic infection will shed light on this issue.

EDITOR DISCLOSURES AT TIME OF PUBLICATION

Disclosures for Stephen G. Baum, MD at time of publication

Consultant/Advisory Board	Clinical Infectious Diseases
Equity	Select Medical Holdings Corp. (no annual income is derived from this equity holding)
Editorial Boards	Medical Letter

CITATION(S):

Lauer SA et al. The incubation period of coronavirus disease 2019 (COVID-19) from publicly reported confirmed cases: Estimation and application. Ann Intern Med 2020 Mar 10; [e-pub]. (https://doi.org/10.7326/M20-0504)