COVID-19 exposure on flights is more common than you think. The US doesn't share details, but Canada does

On the day after Christmas, passengers on a United Airlines flight from Denver to Calgary, Alberta, were potentially exposed to COVID-19.

So were travelers on a Delta Air Lines flight from Detroit to Toronto, an Air Canada flight from Fort Lauderdale, Florida, to Montreal and 11 other international flights to Canada.

The next day, another busy holiday travel day, more of the same: 14 flights to Canada from places including Boston; Chicago; Houston; Cancun, Mexico; and the Dominican Republic, all had at least one passenger on board who tested positive for COVID-19 shortly after the flight.

The flights aren't outliers due to the holiday travel rush.

Data from Canadian public health authorities show a near daily occurrence of flights where a passenger may have been infected while flying. From the start of the coronavirus pandemic in March through early January, the Public Health Agency of Canada has identified potential exposure on more than 1,600 international flights and more than 1,400 flights within Canada, for a total of more than 3,000 flights, including nearly 200 in the past two weeks alone.

On the list: U.S. carriers American, United, Delta, Alaska and Allegiant. The U.S. cities with the most affected flights on the list: Chicago, Phoenix, a magnet for Canadian visitors, and Denver.

The details aren't buried in some secret database. Canada has been posting public COVID-19 exposure alerts online for flights, trains and cruise ships throughout the pandemic. Flights are listed as soon as authorities receive word of a positive test of a recent traveler, regardless of where and when they might have been infected, factors that are hard to pinpoint in most COVID-19 cases.

Incidents are posted as little as two days after the flight, so other recent travelers can search to see if someone on their flight tested positive and watch for symptoms. The flights fall off the list after two weeks because of Canada's mandatory 14-day quarantine upon arrival. One major Canadian airline, WestJet, keeps a running list of its affected flights (more than 700 to date) on its website for recent passengers and would-be ticket buyers to see.

"Some people might look at that (disclosure) negatively,'' WestJet spokeswoman Morgan Bell said. "We just thought that transparency was the best thing.''

The publicly available details on COVID-19 on Canada flights, which includes flight date; airline; flight number; origin and destination; and, where available, row numbers because passengers seated within a few rows of an infected passenger are most susceptible to exposure, are in stark contrast to disclosures about impacted flights in the United States.

The Centers for Disease Control and Prevention doesn't publish a list of affected flights, nor do U.S. airlines, who prefer to tout their pandemic safety protocols and studies that show a low risk of virus transmission on planes.

The CDC has revealed little information on the scope of COVID-19 exposure on flights except to release, when requested, the number of affected flights. The latest tally: more than 4,000 flights within and into the United States.

That number has more than doubled since August and compares with infectious disease investigations on just 150 flights in each of 2019 and 2018.

Individual cases show up occasionally on local health department websites, including flights involving Delta and Allegiant passengers arriving in Albany, New York, over the summer. And there are the rare cases of in-flight medical emergencies due to COVID-19, most recently a United Airlines passenger who fell critically ill on a flight from Florida and died shortly after landing. The coroner's report listed COVID-19 as a cause of death.

Another summer case: Texas woman died of COVID on Spirit flight

But those reports don't give travelers the full picture of the regularity with which someone who has been on a plane might have traveled with COVID-19, with or without symptoms, and on which airlines and routes.

Canada's approach has two major public health benefits, according to Dr. Amesh Adalja, senior scholar at Johns Hopkins Center for Health Security.

Allowing the public to easily see if someone on their flight tested positive so they can take the appropriate steps in an effort to stop the spread is essentially public contact tracing, he said.

The regularly updated lists of flights also help would-be travelers, he said.

"It gives someone an idea if they're debating on whether or not to fly, of what the risks are,'' he said. "The more information the public has on the risk of everyday activities, the more informed those activities are going to be.''

Public or not, Adalja says no one should be surprised by the number of cases of airplane passengers likely flying with the virus given the surge in coronavirus cases and the fact that so many cases involve no symptoms or mild symptoms.

Travelers wear face masks at a busy American Airlines concourse at Charlotte-Douglas International Airport in November.
Travelers wear face masks at a busy American Airlines concourse at Charlotte-Douglas International Airport in November.

"You could do the same study on Greyhound buses or Amtrak trains or the subway. The fact is, that with so much community spread, when you go anywhere, you’re going to be around people with COVID,'' he said. "I think that people just don't realize that this virus is everywhere right now. Any activity you do is going to have risk.''

Adalja said the key is mitigating that risk with face coverings, hand-washing and social distancing. The latter is a challenge while traveling, as anyone who spent time at an airport during the holiday season knows. Despite the best efforts of airlines and airports, crowds still form in the usual spots: check-in, gate areas, deplaning and baggage claim.

So why doesn't the U.S. have a more robust public accounting of COVID-19 on planes?

Dr. Martin Cetron, director of the CDC's Division of Global Migration and Quarantine, said COVID-19 has "superpowers'' and is the toughest virus he's fought in nearly 30 years with the CDC.

He said it's nearly impossible to give the public an accurate risk assessment on flying or other activities in "wartime,'' especially as cases surge.

Cetron recalled a tuberculosis case involving a passenger on a flight from Atlanta to Paris in 2007. The CDC raced to get the information out to the public about getting tested and even set up a hotline for fellow passengers to call for more details.

Cetron said he's not sure the agency could do that today with a faster spreading disease and 4,000 flights.

"And who would they call?'' he said, citing underfunding of public health.

State and local health departments, which initiate the contact tracing, are also overwhelmed, he said.

The CDC "could be doing better,'' Cetron said, but he noted that Canada has a fraction of flights to monitor, and travel has been strongly rebounding in the U.S. There were 2.1 million international passenger arrivals between Dec. 1 and Dec. 28, he said, an average of 76,000 passengers a day and quadruple the number of passengers in June.

There were 45,000 scheduled domestic and international flights arriving in Canada in the fourth quarter, compared with 1.2 million in the U.S., according to global aviation data firm Cirium.

Cetron also said publishing the list of flights is not contact tracing; it's the first step in a contact investigation.

"All Canada really does is the first step,'' Cetron said. "That's a notification. We could do that.''

Yet they don't.

Cetron said the CDC, working with local and state health authorities, aims to get more details, he said, tracking down other passengers, educating them on the virus and symptoms to watch for and finding out if other passengers on the flight end up getting sick to see how and if the virus spread among passengers. He called it a cumbersome process, where people drop out through the process because they can't be reached or don't respond to requests for information.

Officials often run out of time because the longer it takes to start a contact investigation after a known exposure, the more time there is for the disease to spread, he said. Most contagiousness peaks in the first week after exposure.

"If you can't get the whole thing done in four days, it becomes an exercise in futility,'' he said.

Cetron said he thinks the best approach for the CDC when it comes to information on activities like travel during the pandemic is to suggest ways to reduce the risk of getting COVID-19.

The CDC's advice on travel, which has gained an urgent tone since Thanksgiving: Don't do it. And the agency is not just talking about flying. Travel is a "door-to-door'' experience, Cetron said, with potential exposure from the ride to the airport to the car rental shuttle and hotel.

"Trust us, this is not the time to be traveling,'' he said, adding that pandemic record holiday travel volumes "broke his heart.''

CDC advice: Avoid holiday travel, get COVID tests if you do go away

Airlines say it's safe to fly during pandemic

Airlines for America, the U.S. airline industry's trade group, said airlines have relied on science to help protect passengers during the pandemic.

"U.S. airlines have implemented multiple layers of measures aimed at preventing virus transmission on board the aircraft, including strict face-covering requirements, enhanced disinfection protocols and hospital-grade ventilation systems,'' Katherine Estep, the group's spokeswoman, said in a statement. "We remain confident that this layered approach significantly reduces risk and are encouraged that science continues to confirm there is a very low risk of virus transmission on board aircraft."

Estep also pointed to mandatory pre-departure health forms airlines have added in a bid to keep ill passengers from traveling.

Airlines ask passengers a series of health questions during online check-in or at the airport. Delta calls it "Your commitment to safety'' and asks them to pledge that they have not been diagnosed with or exposed to COVID-19 within the past 14 days; have not had any of the primary symptoms in the past 14 days; and will wear a face covering throughout the airport and on the plane.

Alaska Airlines' online health agreement.
Alaska Airlines' online health agreement.

Alaska calls it a "health agreement' and asks passengers to certify that they will wear a mask, have not been diagnosed with COVID-19 within the past 21 days, have experienced no COVID-19-related symptoms within the past 14 days, have not been denied boarding by another airline due to a medical screening for a communicable disease for the past 14 days, have not had close contact with someone who tested positive for COVID-19 within the past 14 days and, that if they feel ill after check-in but prior to the fight, they will not travel. It urges travelers to rebook if they don't meet the criteria.

But passengers are on the honor system. United said the passenger who died said on his form that he did not have the virus or any symptoms. Yet fellow passengers who documented the in-flight emergency on Twitter said he appeared sick.

Preflight COVID-19 testing: The answer to keeping sick passengers off planes?

Travelers who haven't been on a plane during the pandemic are often surprised to find out U.S. airlines aren't checking passengers for COVID-19 symptoms – only Frontier takes passengers' temperatures, and it says the number of travelers denied boarding due to fever is minimal. And most aren't aware that passengers don't actually have to present a negative COVID-19 test before boarding except for scattered international destinations with entry restrictions, including some Caribbean resorts.

Some U.S. destinations, including Hawaii, require proof of a negative COVID-19 test to visit without quarantining. Travelers must receive the results before their flight departs, but they don't have to show proof until they land and are met by local health authorities.

The preflight testing scene is changing rapidly, though, a move designed to reduce the number of flights carrying passengers who may be infected.

As of Jan. 7, Canada requires all travelers ages 5 and older to provide proof of a negative coronavirus test to the airline before boarding a flight to Canada. And, notably, they still have to quarantine for 14 days.

The U.S. will join the testing club on Jan. 26. The CDC announced Tuesday that all passengers over the age of 2, including U.S. citizens, boarding an international flight to the United States will have to show proof they tested negative no more than three days prior to their flight or have recovered from COVID-19. Those who don't will be denied boarding. There is no universal requirement in place for flights from and within the United States, and Delta Air Lines CEO Ed Bastian said on Thursday that he doesn't see that happening.

The fine print: What to know about new COVID testing rules on flights to US

Adalja is a fan of preflight testing, the closer to departure the better.

"I do think it's better than what we're doing right now,'' he said.

Testing is not foolproof, of course. There can be false negatives (and false positives), and travelers could become infected after they have their test but before they board their flight.

And despite what airlines call a low risk of onboard transmission, it has happened, even with mandatory pre-departure testing and in-flight mask requirements. New Zealand health officials found a cluster of coronavirus cases genetically linked to one passenger, who didn't have any symptoms, traveling on an 18-hour flight from Dubai to New Zealand in September.

A report on the flight in the CDC's Emerging Infectious Diseases Journal, released last week concludes: "Although not definitive, these findings underscore the value of considering all international passengers arriving in New Zealand as being potentially infected with SARS-CoV-2, even if predeparture testing was undertaken, social distancing and spacing were followed, and personal protective equipment was used in-flight.''

This article originally appeared on USA TODAY: COVID flight info: Passengers on 7,000 US, Canadian flights exposed