Testing upon exit of quarantine — ideally around day six or seven — is more effective than upon entry, and testing twice could make an eight-day quarantine as effective as a 14-day one
Aspeople in the United States ponder how to safely reunite with family for Thanksgiving, a new study that includes data from offshore oil rig workers could help clarify the best strategy.
The matter of reuniting with family for the holiday is fraught. The nation’s top infectious disease expert, Dr. Anthony Fauci, has urged Americans to skip Turkey Day altogether. Data from Canada, where Thanksgiving is celebrated in October, underscore the risks of gathering in big groups for the occasion. Canadian public health officials attributed an acceleration of Covid-19 cases there to the festivities. It’s perhaps no surprise, then, that in the United States, a poll found that 21% of people have put their regular Thanksgiving travel plans on pause — yet 39% still intend to travel during the holiday.
Many epidemiologists have recommended a two-week quarantine before gathering with loved ones to prevent spreading the coronavirus during Thanksgiving. Two weeks is also the amount of time that both the U.S. Centers for Disease Control and Prevention (CDC) and the World Health Organization recommend to spend in quarantine if you have been exposed to someone who has tested positive for the SARS-CoV-2 virus that causes Covid-19. (This is different from self-isolation for people who have tested positive, which lasts around 10 days and is shorter given that the incubation period has already passed.) Among people infected with the coronavirus, around 98% of people will develop symptoms by day 12 of quarantine, some research has shown, and the median incubation time is five days.
“It makes no sense to use unduly restrictive quarantines while at the same time having indoor dining.”
But given the financial and mental health downsides to long quarantines, some rules for travel-related quarantineare changing. The CDC moved away from a blanket 14-day quarantine for international travelers at the end of summer. On November 3, New York implemented new guidelines allowing travelers from out of state to test out of the mandatory 14-day quarantine if they obtain two negative tests — one before their journey to the state begins and another four days after. Meanwhile, Alberta, Canada, is piloting a program in which certain travelers can do a test at the airport. Participants can leave their quarantine if and when the results come back negative, which usually takes two days, and they must also obtain a second test four or five days after that.
Now, however, researchers say they have combined data about various aspects of Covid-19 that offers a more complete picture of how to shorten the standard 14-day quarantine.
In a new study, Jeffrey Townsend, a biostatistician at the Yale School of Public Health, and his collaborators created a model using existing data on how infectious people with Covid-19 are at different points of their illness, along with information about the accuracy of so-called PCR tests for the disease at those time points. Crucially, the model also takes into account data from other studies about the incubation period of SARS-CoV-2. This last bit is especially important given that infected individuals can spread the disease several days before they begin to feel ill (and some infected people never develop symptoms).
The study, which was originally posted online on October 28 and has not yet been vetted by other scientists for publication in a scientific journal, suggests that an eight-day quarantine in which people are tested upon entry on day one and again on day seven before exiting on day eight (given that it typically takes a day for PCR test results) is just as effective as a 14-day quarantine without testing. It’s not possible to test twice in many places, however, and so the authors also modeled whether it would be better to test before or during quarantine. They concluded that testing upon exit of quarantine — ideally around day six or seven, when the amount of virus in the body has risen to detectable levels — is more effective than testing upon entry.
The results are in line with a previous study from a British group posted online this summer that, based on modeling simulations, suggested an eight-day quarantine with PCR testing on day seven would provide similar protection to a 14-day quarantine period. However, the new study from Townsend and his colleagues went a step further and validated some of its findings by testing the recommendation with Australian company BHP, which does offshore oil drilling.
BHP had already been requiring its workers to quarantine at a hotel on land before deploying to the drilling site offshore as a precaution, since conditions on the rig involve tight living and working quarters where Covid-19 could easily spread. But the study findings prompted the company to implement exit testing as well. “They were incredibly receptive” to the change, Townsend says. After the new protocol was put in place, it identified 16 out of 1,026 individuals who tested negative on the entry test but then tested positive in the second test. Without the second test, they might not have been detected as having the virus and would have left for the offshore rigs. Townsend says he’s heard that the news about the importance of exit testing is making other firms rethink their approach: “Other oil companies heard about how well the BHP work was going in preventing outbreaks, and this [approach] migrated through the industrial sector.”
“I think these findings are consequential, as they provide a path to making quarantine less burdensome for people.”
The new study’s proposal to shorten the 14-day quarantine using carefully timed testing is a move in the right direction, says David Fisman, an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health. “This makes total sense,” Fisman says. “We know Covid crosses borders. It makes no sense to use unduly restrictive quarantines while at the same time having indoor dining,” he adds, noting that more concern should be directed to the potential of superspreading events in the latter situation.
“I think these findings are consequential, as they provide a path to making quarantine less burdensome for people,” says Angela Rasmussen, a virologist at Columbia University. “However, this depends heavily on testing capacity. Without sufficient testing, this won’t be feasible.” Laboratories across the United States have had a tough time keeping up with demands for Covid-19 testing.
Townsend, for his part, says his family has no travel plans and is staying isolated at home for Thanksgiving. “Being an epidemiologist doing this kind of work, you would feel like a hypocrite if you didn’t take the most extreme precautions,” he says. Townsend adds, though, that his wife and three kids will still mark the occasion, albeit in a scaled-down version: “We are going to have a Thanksgiving meal, and it’ll be fun and it’ll be great.”