The symptoms of the novel coronavirus usually take five days to show in an infected person, a new study has found.
The study, published on Monday in the journal Annals of Internal Medicine, looked at 181 cases of COVID-19 in China and other countries in order to estimate the length of the virus’s incubation period.
Researchers from Johns Hopkins Bloomberg School of Public Health said the average incubation time was 5.5 days.
The study said, though, that the incubation period could differ for milder cases.
The new coronavirus was first detected in China late last year. Since then, it has spread around the globe, infecting more than 118,000 people and claiming more than 4,000 lives as of Tuesday afternoon.
Researchers conducted the study early in the COVID-19 outbreak, when community transmission was limited to Wuhan, China — the city believed to be the epicentre.
This allowed them to track when an individual was exposed to the virus. They were able to use this data to estimate the virus’s incubation period.
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“We have sort of a narrow window at the beginning of the epidemic to really tease out what’s going on,” the study’s senior author Justin Lessler, an associate professor in the Bloomberg school’s department of epidemiology told CNN. “If it’s everywhere, you don’t know where people got infected.”
The study suggests that the current recommended 14-day quarantine period for COVID-19 patients is “reasonable,” because in 97.5 per cent of cases studied, patients experienced symptoms within 11.5 days.
“Based on our analysis of publicly available data, the current recommendation of 14 days for active monitoring or quarantine is reasonable, although with that period some cases would be missed over the long-term,” Lessler said in a press release.
The study said, though, that in extreme cases, a longer quarantine period might be justified, with 101 out of every 10,000 infected individuals developing symptoms after the 14-day period.
Stanley Perlman, a coronavirus expert at the University of Iowa, who was not a part of the study, told Global News knowing a virus’s incubation period not only allows health officials to “hone down” on an appropriate incubation period, and also helps to determine the risk.
“If you’re around someone who you find out later had the disease, you can personally feel comfortable at the five-day mark knowing, ‘OK, I’ve already passed the 50 per cent mark of where I’m likely to get the disease,'” he said. “And then as the days go on, you feel more comfortable and you feel more comfortable being around your family, going back to work. So that’s where this really helps a lot.”
He said identifying the incubation period can also help officials track down people who have been in contact with a patient so they can be tested.
Perlman said the issue is that during the incubation period, if a person is not showing symptoms, they could pass through screening measures undetected.
“If you’re on an airplane sitting next to someone, for example, and he’s just brewing the disease, he could be contagious and you may pick it up,” he said. “You may not be ill for several days.”
He explained, though, that if a patient is “completely asymptomatic” and is not showing any clinical signs, they are “really minimally contagious.”
“The incubation period is how long it takes you after exposure to get sick, so it doesn’t necessarily mean when you are contagious,” he said. “You’re going to be most contagious as you get near to being sick.”
Overall, Perlman said the study’s “decent” sample size has produced an estimated incubation period “within the same range” as other human coronaviruses in the past.
“They’re all really very similar,” he said.
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