Although a 14-day quarantine after exposure to novel coronavirus is “well supported” by evidence, some infected individuals will not become symptomatic until after that period, according to authors of a recent analysis published in Annals of Internal Medicine.
Most individuals infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) will develop symptoms by day 12 of the infection, which is within the 14-day period of active monitoring currently recommended by the Centers for Disease Control and Prevention, the authors wrote.
However, an estimated 101 out of 10,000 cases could become symptomatic after the end of that 14-day monitoring period, they cautioned.
“Our analyses do not preclude that estimate from being higher,” said the investigators, led by Stephen A. Lauer, PhD, MD, of Johns Hopkins Bloomberg School of Public Health, Baltimore.
The analysis, based on 181 confirmed cases of coronavirus disease 2019 (COVID-19) that were documented outside of the outbreak epicenter, Wuhan, China, makes “more conservative assumptions” about the window of symptom onset and potential for continued exposure, compared with analyses in previous studies, the researchers wrote.
The estimated incubation period for SARS-CoV-2 in the 181-patient study was a median of 5.1 days, which is comparable with previous estimates based on COVID-19 cases outside of Wuhan and consistent with other known human coronavirus diseases, such as SARS, which had a reported mean incubation period of 5 days, Dr. Lauer and colleagues noted.
Symptoms developed within 11.5 days for 97.5% of patients in the study.
Whether it’s acceptable to have 101 out of 10,000 cases becoming symptomatic beyond the recommended quarantine window depends on two factors, according to the authors. The first is the expected infection risk in the population that is being monitored, and the second is “judgment about the cost of missing cases,” wrote the authors.
In an interview, Aaron Eli Glatt, MD, chair of medicine at Mount Sinai South Nassau, Oceanside, N.Y., said that in practical terms, the results suggest that the majority of patients with COVID-19 will be identified within 14 days, with an “outside chance” of an infected individual leaving quarantine and transmitting virus for a short period of time before becoming symptomatic.
“I think the proper message to give those patients [who are asymptomatic upon leaving quarantine] is, ‘after 14 days, we’re pretty sure you’re out of the woods, but should you get any symptoms, immediately requarantine yourself and seek medical care,” he said.
Study coauthor Kyra H. Grantz, a doctoral graduate student at the Johns Hopkins Bloomberg School of Public Health, said that extending a quarantine beyond 14 days might be considered in the highest-risk scenarios, though the benefits of doing so would have to be weighed against the costs to public health and to the individuals under quarantine.
“Our estimate of the incubation period definitely supports the 14-day recommendation that the CDC has been using,” she said in an interview.
Dr. Grantz emphasized that the estimate of 101 out of 10,000 cases developing symptoms after day 14 of active monitoring – representing the 99th percentile of cases – assumes the “most conservative, worst-case scenario” in a population that is fully infected.
“If you’re looking at a following a cohort of 1,000 people whom you think may have been exposed, only a certain percentage will be infected, and only a certain percentage of those will even develop symptoms – before we get to this idea of how many people would we miss,” she said.
The study was supported by the Centers for Disease Control and Prevention, the National Institute of Allergy and Infectious Diseases, the National Institute of General Medical Sciences, and the Alexander von Humboldt Foundation. Four authors reported disclosures related to those entities, and the remaining five reported no conflicts of interest.
SOURCE: Lauer SA et al. Ann Intern Med. 2020 Mar 9. doi:10.1101/2020.02.02.20020016.