Routine testing for asymptomatic SARS-CoV-2 at airports could catch nearly 90% of travelers before they attempt to board a plane, a new modeling study suggests.
Computer simulations also showed that most imported infections could be prevented with a combination of pre-travel testing and a five-day post travel quarantine that would only lift with a negative test result, according to the report published in The Lancet Infectious Diseases.
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The model assessed what would happen if a cohort of 100,000 airline travelers was tested or not tested, and whether the addition of quarantining after travel was effective in preventing the spread of COVID-19 to the traveler’s destination.
“Getting tested before you travel and often after you travel, can really reduce the risk of COVID with air travel,” said the study’s lead author, Nathan Lo, a resident physician and incoming faculty fellow in infectious diseases at the University of California, San Francisco. But, “we should still only travel when it’s essential.”
To take a look at the feasibility of using testing and quarantining to catch infectious people prior to boarding planes and stop infectious people who slip through that screening from spreading the disease at their destination, the researchers built a model to simulate several scenarios.
The simulation involved 100,000 hypothetical individuals and publicly available data on COVID-19 clinical cases as well as published natural history parameters that allowed individuals to be assigned to one of five health states: susceptible to infection, latent period, early infection, late infection, and recovered. The researchers estimated a per-day risk of infection with the virus corresponding to a daily incidence of 150 infections per 100,000 people.
They assessed five testing strategies: (1) anterior nasal PCR test within three days of departure, (2) PCR within three days of departure and five days after arrival, (3) rapid antigen test on the day of travel (assuming 90% of the sensitivity of PCR during active infection), (4) rapid antigen test on the day of travel and PCR test five days after arrival, and (5) PCR test five days after arrival.
Strategies two and four included a five-day quarantine after arrival. The travel period was defined as three days before travel to two weeks after travel. Under each scenario, individuals who tested positive before travel were not permitted to travel.
The model suggested that in a scenario with no testing or screening, there would be 8,357 infectious days with 649 actively infectious passengers on the day of travel. The pre-travel PCR test reduced the number of infectious days from 8,357 to 5,401, a reduction of 36% compared with the base case, and identified 569 (88%) of 649 actively infectious travelers on the day of flight; the addition of post-travel quarantine and PCR reduced the number of infectious days by 70% to 2,520.
The rapid antigen test on the day of travel reduced the number of infectious days to 5,674 (-32%) compared with no screening, and identified 560 (86%) actively infectious travelers; the addition of post-travel quarantine and PCR reduced the number of infectious days to 3,124, a reduction of 63% compared with no screening. The post-travel PCR alone reduced the number of infectious days by 42%, to 4,851.
The new study is “very interesting,” said Dr. Waleed Javaid, a professor of medicine at the Mount Sinai School of Medicine at Mount Sinai in New York City, hospital epidemiologist, and director of infection prevention and control at the Mount Sinai Downtown Network. “But is it ok to travel if there is a 10% chance of having an infectious person on the plane?,” Dr. Javaid asked.
The problem is that all the tests are imperfect, Dr. Javaid said. “If I am exposed to someone with COVID two days later the test is likely to be negative even if I’ve been infected,” he explained.
For the tests to come out positive the person needs to have a high enough level of virus in their respiratory system, Dr. Javaid said. If people need to travel, even if all of this screening is done, “the bottom line is they need to keep their guard up, wear masks, practice good hand hygiene and social distancing. They also need to be aware when someone is visibly ill and stay away from that person.”
The first SARS virus taught us that the disease can be spread on planes, Dr. Javaid said. And that goes for other respiratory illnesses as well, he added.