The largest study of coronavirus patients so far suggests it could take up to 24 days after exposure for symptoms to show
- The coronavirus outbreak that originated in Wuhan, China, has killed at least 1,370 people and infected more than 60,000 people.
- New research from a group of Chinese scientists suggested the virus' incubation period — the time between exposure and the onset of symptoms — could be as long as 24 days.
- The Centers for Disease Control and Prevention says the coronavirus' incubation period is two days to two weeks.
- Based on that estimate, the CDC instituted a 14-day federal quarantine for the US citizens evacuated from Wuhan. The new study raises doubts about whether that's enough.
- Visit Business Insider's homepage for more stories.
The novel coronavirus that originated in Wuhan, China, in December has killed at least 1,370 people, infected more than 60,000 people, and spread to 25 other countries.
As researchers race to learn more about the virus, a crucial question lingers: How much time passes between when a person gets infected and when their first symptoms appear?
"Every day there are new estimates coming out for the incubation period," Lauren Ancel Meyers, a professor of integrative biology at the University of Texas at Austin, told Business Insider.
According to the Centers for Disease Control and Prevention, the incubation period is believed to be two to 14 days.
But research published on Sunday from a group of Chinese scientists led by Zhong Nanshan, who discovered the SARS virus, suggests it might take as long as 24 days for a person to start showing symptoms after being exposed to the novel coronavirus. The study examined 1,099 coronavirus cases from 522 hospitals across 31 provinces in China, making it the largest coronavirus case study to date, though it has not yet been peer-reviewed.
Meyers said uncertainty about the incubation period "is particularly relevant when you're thinking about how long you actually have to monitor people to make sure that they're not infected."
So far, the US and many other countries have been formulating quarantine rules based on a 14-day incubation period.
US citizens evacuated from Wuhan last month were brought to military bases in nine states, including California and Texas, where they were put under a mandatory 14-day quarantine. On Tuesday, 195 of those evacuees were permitted to leave the March Air Reserve Base in Riverside, California, marking the first successful US quarantine in nearly 60 years.
The UK, Australia, France, India, Italy, and Canada have also said that citizens repatriated from Wuhan will be quarantined for 14 days. And on Monday, the UK government announced measures allowing for a mandatory 14-day quarantine of coronavirus patients.
"It's widely accepted that there's a 14-day rule of thumb," Stephen Morse, an epidemiologist at Columbia University, told Business Insider. "That's how long you have to wait to go back to your daily life."
But if this new study is correct, 14 days may not be sufficient.
Is a 14-day quarantine long enough?
In the new study, the median age of patients was 47 and the median incubation period was three days, though the full range of incubation periods was zero to 24 days.
CDC officials have said they're confident that the 195 evacuees' two-week isolation was long enough.
"The incubation period is obviously really important for us as we look to make sure that we're releasing these people safely from quarantine," Nancy Messonnier, the director of the CDC's National Center for Immunization and Respiratory Diseases, said in a Wednesday press briefing.
"We still think that for today, for now, 14 days is the right interval to use," she added.
Michael Ryan, the executive director of the World Health Organization's health-emergencies program, said this week that the WHO was also "not considering changing anything" about its quarantine recommendations.
Pinpointing the incubation period is difficult and important
Identifying a virus' incubation period is critical for modeling its spread.
"It gives you an idea of how quickly the virus could propagate, if you want to project how many patients you're going to see," Morse said.
Morse added that there were a few reasons to be skeptical of the 24-day estimate in the new study. "Was this one patient or a significant number that experienced a 24-day incubation period?" he said.
The research didn't specify how many patients had incubation periods longer than two weeks.
What's more, Morse said, the 24-day figure could have been based on inexact data.
"These are largely patients who have been found through hospitalization," he said. "So we don't know how long they've had the virus based on when they went to hospital. We have to rely on their memory of when they were exposed, which may or may not be accurate."
Morse also questioned the lower end of the incubation-period range in the study.
"Zero days makes me suspect — does that mean patients are developing symptoms the same day as contact?" he said. "One to two days I can accept, but less than 24 hours seems extreme."
Ryan mentioned another possible explanation for the longer-than-expected incubation period in the study.
"A very long incubation period can reflect a double exposure," he said.
Source: Read Full Article