March 12, 2020

Median COVID-19 Incubation Period Is 5.1 Days

By Denise Baez

The median coronavirus disease 2019 (COVID) incubation period was estimated to be 5.1 days and 97.5% of those who developed symptoms did so within 11.5 days of infection, according to a study published in the Annals of Internal Medicine.

“These estimates imply that, under conservative assumptions, 101 out of every 10,000 cases will develop symptoms after 14 days of active monitoring or quarantine,” wrote Stephen A. Lauer, MD, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, and colleagues. “Our results support current proposals for the length of quarantine or active monitoring of persons potentially exposed to COVID-19, although longer monitoring periods might be justified in extreme cases.”

For the study, the researchers pooled data from 181 confirmed cases of COVID-19 that were reported between January 4, 2020, and February 24, 2020 from 50 provinces, regions, and countries outside Wuhan, China. Most of the cases involved travel to or from Wuhan. The researchers studied patient demographic characteristics and dates and times of possible exposure, symptom onset, fever onset, and hospitalisation.

The median incubation period was estimated to be 5.1 days (range, 4.5-5.8 days) and 97.5% of those who developed symptoms did so within 11.5 days (range, 8.2-15.6 days).

“Although it is essential to weigh the costs of extending active monitoring or quarantine against the potential or perceived costs of failing to identify a symptomatic case, there may be high-risk scenarios where it could be prudent to extend the period of active monitoring, such as a health care worker who cared for a COVID-19 patient while not wearing personal protective equipment,” the authors noted.

The researchers have published an online tool that allows public health officials and members of the public to estimate how many cases would be caught and missed under different quarantine periods. The app can be found here:


SOURCE: Annals of Internal Medicine
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