Youth sports have experienced few coronavirus outbreaks so far. Why is ice hockey so unlucky?

When a youth hockey coach in Texas died in August from the coronavirus, Steve Bellemore hoped it was just a chance tragedy. Then the winter season began, and outbreaks linked to the sport exploded.

Massachusetts logged more than 100 youth hockey cases in a few weeks. In Maine, an asymptomatic referee exposed up to 400 people in two days. In Bellemore’s home state of New Hampshire, state officials shut down youth hockey for two weeks to get cases under control and mandated testing for all 20,000 players - a directive that resulted in long lines and other chaos at testing centers statewide.

“Whole hockey teams are getting quarantined,” said Bellemore, a hockey parent, coach and president of the Manchester Youth Regional Hockey Association. “It’s getting very real.”

State officials and other authorities have been scrambling to mitigate the damage: On Nov. 12, seven governors in the Northeast banded together to ban all interstate youth hockey until at least the end of the year. The following week, health officials in Minnesota, where hockey is associated with the most clusters of any youth sport, put all sports on “pause” for four weeks. Many others have imposed new restrictions and safety measures on the game.

[Hundreds of potential coronavirus quarantines around Alaska in the wake of youth hockey tournament]

Youth sports - soccer, basketball, cross-country, swimming, whether held indoors or out, a source of American pride, prestige and bonding - were among the first group gatherings to be allowed post-lockdown. Organizers worked closely with public health officials to make modifications that balance safety with maintaining the spirit of the games. This has worked to some extent.

While public health officials suspect off-field interactions may be contributing to community spread, there’s little hard data. In most areas, there have been few to no documented outbreaks, much less superspreader events.

Ice hockey is an anomaly. Scientists are studying hockey-related outbreaks hoping to find clues about the ideal conditions in which the coronavirus thrives - and how to stop it. Experts worry that ice rinks may trap the virus in an area that, by design, restricts airflow, temperature and humidity.

The hockey-related cases have been especially striking, epidemiologists have said, because clubs followed Centers for Disease Control and Prevention limits on gathering size and had numerous social distancing measures in place. In retrospect, one mistake by some clubs was that until recently masks had only been required on ice for the two players doing the initial faceoff for the puck - although many players wore clear face shields, which theoretically should have a similar effect.

“We’re watching hockey very carefully because it’s the first major sport that’s been played indoors predominantly and also during the winter months,” said Ryan Demmer, an epidemiologist at the University of Minnesota’s School of Public Health.

Demmer said the cases provide some of the first real-world evidence to support early theories about the importance of how people breathe, ventilation, and the social dimensions of transmission.

One critical way hockey differs from other contact team sports is how players do line changes - substitutions of groups of players - and are expected to sprint for nearly the whole time they are on the ice. Experts say it likely leads to heavier breathing, resulting in more particles being exhaled and inhaled.

Jose-Luis Jimenez, an air engineer at the University of Colorado, speculated that the spaces occupied by rinks keep the virus suspended, perhaps six to nine feet, just above the ice. Similar outbreaks have been documented in other chilly venues - meat processing factories and at a curling match earlier in the pandemic.

“I suspect the air is stratified,” he said. “Much like in a cold winter night, you have these inversions where the cold air with the virus which is heavier stays closer to the ground. That gives players many more chances to breathe it in.”

Timothy McDonald, public health director in Needham, Mass., said we should not rule out the way kids socialize - in locker rooms, carpools and postgame gatherings - as potential contributing factors. By late October, his area had seen at least six coronavirus cases related to sports clusters that span a wide range of ages, from fifth-graders to high school sophomores. He said some of those children played on multiple sports teams, including hockey.

“We’ve seen a lot of people mingling after the game or having discussions and parents talking and letting kids play around after the game,” he said. “There’s no way to tell from our perspective whether it’s on the ice - or waiting for 10 or 15 minutes while everyone talks after the game.”

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When schools shut down in March, there was huge confusion about the extent to which children could get the virus and transmit it to others. Today, cases among those under 18 years old are soaring. The American Academy of Pediatrics reported last week that more than 1.3 million children had tested positive for coronavirus during the pandemic. Nearly 154,000 children tested positive from Nov. 19 to Nov. 26.

Epidemiologists are uncertain where most of these transmissions are occurring, but early reports from the United States, bolstered by more robust data from Europe and Asia, suggest they are unlikely to be related to school. Emily Oster, a professor of economics at Brown University who has been tracking coronavirus outbreaks in schools, and others say they believe informal neighborhood get-togethers, youth sports and other activities may be contributing.

Rhode Island, for example, has reported that virtual-only learners are being infected at similar rates as those attending in-person school. Oster said infection rates seem to be going up nationwide, “whether schools are open or not.”

Joseph Allen, a researcher at the Harvard T.H. Chan School of Public Health, said he believes it was a mistake for school sports to shut down because kids need physical activity and some for-profit businesses filling the gaps may be operating in a way where “controls may not be as stringent.”

“Not having sports in schools ultimately leads to wider contact networks for many kids,” he explained.

David Rubin, director of the PolicyLab at the Children’s Hospital of Philadelphia, said the “disease reservoir was lower” related to kids in the early fall, suggesting that sports played at that time - namely, soccer - weren’t contributing much to spread. “We saw very little transmission on the field of play,” he said.

“In winter sports, you now add the indoor element. And I think there’s a fair amount of concern that hockey certainly has transmission around the game,” he said.

A PolicyLab blog post last month recommended that if youth sports leagues want to preserve any opportunity to keep playing, they need to enact mandates that strictly curtail all off-field interaction. Even then, “the potential for on-field spread may be too overwhelming to continue safely with team competition during periods of widespread community transmission, and may need to be sacrificed to preserve in-school learning options, at least until early spring or transmission rates decrease substantially.”

When children’s sports started up again this summer, tensions flared among health officials, sports providers and families over which safety measures were necessary and which were over the top. In the pandemic world, soccer was sometimes played seven-on-seven instead of 11-on-11, and with kick-ins instead of throw-ins; basketball with every other spot in free throw lineups empty; swim practices with some kids starting in the middle of lanes to ensure adequate spacing; cross-country with runners racing in small flights to minimize interactions.

But these modifications sent some families “jurisdiction shopping” to find places that allowed games to proceed in their pure form as they had before the virus outbreak, and this was a part of the story of what happened with hockey in New England.

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Ice hockey is part of the culture in this area of the country. Some kids get their first skates almost as soon as they can walk, and family weekends revolve around games. In the aftermath of the first wave of the virus, clubs in numerous states, including Massachusetts, introduced safety measures such as no checking at the younger levels, physical distancing in locker rooms and masks for the two kids doing the faceoffs.

Massachusetts Hockey President Bob Joyce said families who didn’t like those new rules took their children to play in neighboring states with fewer restrictions. And sometimes those players played on multiple teams or had siblings who did and went to school, creating very large social networks.

“It was a wake-up call,” Joyce said. He said state officials estimated that those 108 initial hockey cases amounted to 3,000 to 4,000 others potentially exposed.

In an October report, the CDC detailed a large outbreak in Florida among amateur adult hockey players on two teams that played each other but had no other contact. Investigators speculated that the indoor space and close contact increased the infection risk. They also pointed out that ice hockey “involves vigorous physical exertion accompanied by deep, heavy respiration, and during the game, players frequently move from the ice surface to the bench while still breathing heavily.”

Surrounded by plexiglass not only to prevent errant pucks but to keep the airflow stable so the ice can remain cold, there’s little ventilation and humidity by design in ice rinks. The surface of the ice is kept somewhere around 20 degrees Fahrenheit, the ambient air temperature in the 50s. The Department of Homeland Security has shown in lab experiments that the virus may live at those temperatures up to two times longer in the air. At 86 degrees, for example, 99% of the airborne virus is estimated to decay in 52 minutes. But at 50 degrees, it would take 109 minutes.

William Bahnfleth, a professor of architectural engineering at Penn State University, said there is growing evidence that humidity may play an important role. In higher humidity, the virus attaches to bigger droplets that drop faster to the ground, decreasing the chance that someone will inhale them. The drier the air the faster droplets will evaporate into smaller sized particles that stay in the air, increasing the concentration.

“There are some researchers have come to believe that humidification is the key above all,” he said.

Studies have shown that the virus doesn’t survive as long in the humid air, and that we’re more susceptible to viruses when the air is drier. Separately, epidemiological data from a long-term care facility has shown a correlation between lower humidity and higher infection rates.

Rubin, who is a pediatrician in addition to his public policy research job, said he worries those on the ice may be inhaling larger doses of the virus due to these environmental conditions, making it more likely they will become infected.

“It’s very hard to sort out, but you wonder if increased inoculum of the virus is an extra factor,” he said.

Demming expressed similar thoughts: “It could be infection rates are common across sports, but in a sport like hockey where you are trapping more virus in the breathable air it could result in more severe infections that end up being symptomatic.”

The National Hockey League was able to complete its playoffs after players were put in a bubble where they were tested each day, administered symptom checks and temperature screenings. No cases were reported. But conducting such rigorous screening on the roughly 650,000 amateur players and officials in the United States is an impossible task.

In Vermont, an outbreak at a single ice rink ripped through the center of the state, affecting at least 20 towns in at least four counties, and seeding other outbreaks at several schools. By Oct. 30, when Vermont Republican Gov. Phil Scott detailed the outbreak at a press briefing, 473 contacts had been associated with it.

“One case,” Scott emphasized, “can turn one event into many.”

For Tyler Amburgey, a 29-year-old coach in Lavon, Texas, north of Dallas, the coronavirus started out like a cold. But then it soon progressed to a headache, fatigue and shortness of breath. Authorities later determined that the outbreak spanned several teams and 30 people. By the third day of his illness, Aug. 29, several of Amburgey’s players had tested positive and he was so ill that he canceled hockey practice.

Later that day his wife found him in his bed, unresponsive, and called 911. His heart had stopped, relatives told media outlets, and paramedics were unable to revive him.