People infected with the SARS-CoV-2 novel coronavirus may not manifest symptoms for an average of five days, although most will develop symptoms by 12 days after infection, according to a study published March 9 in the Annals of Internal Medicine.
The findings support recommendations from the U.S. Centers for Disease Control and Prevention (CDC) stating that patients should be actively monitored for 14 days after an exposure to the virus, wrote a team led by Stephen Lauer, PhD, of Johns Hopkins Bloomberg School of Public Health.
Understanding the incubation period of the virus that causes the novel coronavirus disease (COVID-19) is crucial to its control, but this information has not yet been fully established, the authors wrote. Two early analyses estimated incubation time for the virus to be a mean of six days (range, 2-11 days) and a median of five days (range, 2-14 days), respectively. Lauer's group sought to evaluate and, if possible, verify such estimates.
"The incubation period can inform several important public health activities for infectious diseases, including active monitoring, surveillance, control, and modeling. ... Understanding the length of active monitoring needed to limit the risk for missing SARS-CoV-2 infections is necessary for health departments to effectively use limited resources," the authors wrote.
The study consisted of an analysis of 181 confirmed COVID-19 cases reported between January 4 and February 24, data for which came from news reports and press releases from 50 provinces, regions, and countries outside of Wuhan, China. The researchers assessed patient demographic characteristics, dates and times of possible exposure, symptom onset, fever onset, and hospitalization.
Of the 181 cases, the median incubation period was five days; 97.5% of those who developed symptoms did so within 11.5 days of infection, Lauer and colleagues found. A very small percentage of people (2.5%) showed symptoms within two days.
The CDC's current recommendation for active monitoring of people assumed to be exposed to the coronavirus is 14 days, and the study results support this guidance, the group noted. But longer monitoring may be necessary for some populations.
"Among those who are infected and will develop symptoms, we expect 101 in 10,000 ... will do so after the end of a 14-day monitoring period, and our analyses do not preclude this estimate from being higher," the authors wrote. "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 (for example, a [healthcare] worker who cared for a COVID-19 patient while not wearing personal protective equipment) where it could be prudent to extend the period of active monitoring."