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Coronavirus Symptoms Don’t Surface for 5 to 12 Days: Study

Last Updated: March 09, 2020.

By Dennis Thompson
HealthDay Reporter

MONDAY, March 9, 2020 (HealthDay News) -- Folks who contract COVID-19 will develop symptoms between five and 12 days after their exposure to the new coronavirus, Johns Hopkins researchers report.

Based on data from 181 confirmed cases, the researchers estimate the average incubation period of COVID-19 is about five days.

More than 97% of infected people who develop symptoms will do so within 11.5 days, the researchers concluded.

That's good news, because it means the 14-day quarantine period established by the U.S. Centers for Disease Control and Prevention is "appropriate" and will cover 99% of all infectious cases of COVID-19, said study co-author Kyra Grantz, a graduate student at the Johns Hopkins Bloomberg School of Public Health, in Baltimore.

"We predict a very low probability that even among high-risk individuals we would miss any symptomatic cases after that time," Grantz said.

But a big question mark remains: Can infected people spread the virus to others before they show symptoms or if they never have symptoms?

According to Cleveland Clinic infectious disease expert Dr. Kristin Englund, "We don't know for sure if there is asymptomatic transmission of COVID-19."

The latest study comes as coronavirus fears continue to mount around the world.

There are more than 530 confirmed cases of coronavirus in 35 states in the United States, with 22 deaths, according to the Washington Post.

Globally, there are 109,577 confirmed cases across 104 countries and territories, with 3,809 deaths, the World Health Organization says.

The new study "confirms what we are doing when we are quarantining patients," Englund said.

"That lets us feel comfortable lifting that quarantine at the end of 14 days if the patient doesn't have any symptoms, because the vast majority of people should have symptoms during that time frame if they were infected," Englund said.

According to the CDC, symptoms include fever, cough and shortness of breath.

For the study, the researchers pored over news and public health reports of confirmed COVID-19 cases in areas where the virus had not yet taken root and started community transmission. Cases were collected from 24 countries and regions outside mainland China, and 25 provinces within mainland China that were not part of the initial outbreak.

The research team noted the time of each patient's possible exposure to the novel coronavirus, as well as when they fell ill with COVID-19.

Their estimates imply that only 101 out of every 10,000 cases will develop symptoms after 14 days of quarantine, the study authors said.

These findings, published online March 9 in the Annals of Internal Medicine, are consistent with what other research groups have found, Grantz noted.

"With different data and slightly different methods, we're all getting a pretty similar estimate," Grantz said.

More information

The World Health Organization has more about COVID-19.

SOURCES: Kyra Grantz, graduate student, Johns Hopkins Bloomberg School of Public Health, Baltimore; Kristin Englund, M.D., infectious disease doctor, Cleveland Clinic; March 9, 2020, Annals of Internal Medicine, online

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