Controlling disease outbreaks in the NHL

There have been two outbreaks of the mumps in the last three seasons. Why is this happening, and what is the league doing about it?

Editorial note: This piece was co-written with Atif Kukaswadia, PhD,  a writer for the Public Health Perspectives blog on the PLOS network. This piece is being cross-published on both platforms. Enjoy!


When we think of places for disease outbreaks, a few examples quickly come to mind: classrooms, college dorms, crowded trains. Another suggestion? The confines of the National Hockey League, where players are surrounded by literal blood, sweat, and tears. When you watch a hockey game, you’ll routinely see players spitting, swapping saliva through the sharing of water bottles, sweating -- either through playing the game, using the same towel to dry themselves off, or rubbing their sweaty glove in another player’s face during a scrum. Add to this the intense travel and training schedule, along with the close quarters players are in between games, and this means that, among other things, the NHL is a breeding grounds for illness, even rare ones that do not generally permeate the public sphere.

Mumps would be far down the list of possibilities at first glance. Generally recognized as a childhood illness, mumps all but disappeared in the 1970s after Maurice Hilleman developed a single vaccine for measles, mumps, and rubella (MMR) after each of the individual vaccines became available in 1963, 1967, and 1969 respectively. Shortly after, vaccination schedules for the MMR vaccine were implemented by the many public health agencies, including in Canada and the United States, with the initial recommendation of a single dose for children.

There has been a significant impact on public health since the implementation of the MMR vaccine. Quantitatively, case reports of measles, mumps, and rubella dramatically declined throughout three decades of the vaccine’s availability. Using Canada as an example, national cases went from over 33,000 cases in 1951-55 to <1% of that in 2011-13. Although this was already a huge success, small outbreaks still popped up semi-regularly, prompting public health agencies to implement the universal recommendation of two doses of the MMR vaccine in children since the mid-1990s.


The NHL has had two recent mumps-related encounters: October - December 2014, and January - March 2017; the former being much bigger than the latter. As seen in this fantastic visualization from Global News, the 2014 cases started with three teams: the St. Louis Blues, Minnesota Wild, and Anaheim Ducks. By the holiday season, 15 players from four teams were diagnosed, leading NHL teams to postpone their annual holiday visits to hospitals out of fear that an undiagnosed player could introduce the disease into the hospital. When it was all said and done, 24 players from 5 teams showed symptoms or were diagnosed with the mumps - a relatively large percentage given that there were only 584 cases of mumps reported in the U.S. in 2013. Earlier this year, 8 players from 2 teams were infected -- with the Minnesota Wild appearing again. The effect of this was severe, with Adam Larsson describing it as:

“It came right away for me. My face started growing and the fever came at night. Those four days were probably the worst days in my life so far. It was really bad at one point. I couldn’t eat or anything. I’m glad to be back. I just have to work my energy level up a little bit to where I can play.”

The amount of games missed by players have varied: some, like Ducks star Corey Perry, were briefly hospitalized; Wild defenseman Keith Ballard missed 8 games, but teammate Ryan Suter only missed two; meanwhile, New Jersey Devils forward Travis Zajac was over the illness by the time the team had confirmed that he actually had mumps. As this fan-run database shows, when most NHL teams are worried about players missing half a season due to concussions, tearing of tendons, and a variety of gruesome upper and lower body injuries, illnesses like the mumps aren’t the primary concern of players and their coaches. That being said, a highly contagious illness like the mumps is a serious issue and has consequences that vary from disrupting a player or team’s game-day routine to missing ~3-4 weeks, losing weight, and needing time to recover to get back to 100% -- a hard feat in an already-demanding 82 game schedule. Hockey, like many team sports, often run into trouble with players not wanting to admit that they’re injured, due to fear of lost playing time.


One theory has to do with the age of the players who contracted the illness: all of them were born between 1980 and 1994. Experts who specialize in vaccinations know this as the ‘lost cohort’ of MMR: people born between 1970 and 1994 represent a group with only partial protection against the mumps and are most at-risk. Between 1970 and the mid-90s, a single shot of the mumps vaccine was common, and is estimated to protect 64-80% of people. People belonging to this group lost the immunity they would have developed through childhood exposure to mumps and getting “over it” in the wild like the previous generation. When public health officials noticed that immunity faded with time, they introduced the MMR booster program in the mid-90s for children between the ages of 18 months and 4 years old, and two doses became the standard. This ‘lost generation’ refers to people currently between the ages of 23 and 37, and can explain recent mumps outbreaks in Toronto and the United Kingdom. What’s the average age of an NHL player? 27.3. Thus, despite being super-fit and vaccinated once, our NHL player sample is uniquely vulnerable -- not just because of their environment, but also due to their fading ‘one-shot’ immunity.

Adding to this is the idea of herd immunity. When a critical mass of people are vaccinated and unable to transmit a disease, this protects the unvaccinated e.g., those with compromised immune systems, the elderly or very young, and those who cannot take the vaccine due to previous adverse reactions. However, as we mentioned above, some NHL players would have lost their immunity over time, and thus can no longer count on the benefits of herd immunity to protect them. Add to this how they share confined spaces and equipment with peers, and you have an environment where diseases can be transmitted quickly.


As noted at the beginning of this piece, given the warm, moist, and relatively gross environment surrounding an NHL player, there’s only so much you can do in terms of prevention. What has the league been doing?

The NHL and NHL Players Association (NHLPA) have a joint health and safety committee that work with teams when issues like this come up and issue league-wide memos, which it did twice during the 2014 outbreak. For contagious illnesses like the mumps, this is often through education, such as emails to players with the symptoms and warning signs, setting up voluntary vaccination appointments, and implementing best practices with respect to sanitizing equipment, such as water bottles, jerseys, and dressing room stalls. Interestingly, nothing is mandated, with a statement from the committee encouraging ‘booster shots’ of the vaccine and recommended changes to “bench and locker room behaviour” but noting that decisions for mumps and any other diseases are made at the club level [referring to the NHL’s 31 franchises]. Some clubs are more proactive than others. In Buffalo, as soon as a player shows any sign of sickness, players have to drink from their own water bottles, their equipment is marked, and hospital-strength laundry detergent is used to wash their uniform separately. In Detroit, a portable room sanitizer called the Fresh Gear ActivO has been ordered. The machine is designed to kill mould, viruses, and bacteria using ozone and is mainly used in cases of fire damage, but the Wings use it in the dressing room after every game.


The environment within NHL clubs are relatively controlled, with most players together a majority of the time -- from on-ice, rooming together on the road, and flying with charter planes. Thus, when one player contracts the illness, it’s relatively hard to contain it other than by separating a player out completely. But with mumps having a long incubation period of about 16 to 18 days, although it can be as short as 12 to as long as 25 days (CDC), detecting that an illness is in fact the mumps can be difficult, and by that point, it may already be too late. However, for the public, this controlled environment means that what happens in the NHL may not necessarily pose greater risk. When things go wrong in sports, we generally blame it on the referees, and here, yet again, we can blame referees for increasing the public risk of an NHL mumps outbreak (sort of kidding). The ~66 referees employed by the NHL fly commercially like the rest of the public, waiting around airport terminals and going in-and-out of rinks with the public, potentially leading to increased risk.

The NHL also has to worry about the administrative and logistical challenge of handling the public health of multiple sports leagues, as demonstrated by the 2017 outbreak starting in October 2016 when three members of the New Jersey Devils’ minor league affiliate (AHL) in Albany, New York contracted the illness. When players are traded to other teams, or players are called up for a game and sent back down, they may carry bacteria from their previous environment.

The fact that the players diagnosed with the mumps in 2014 and 2017 were born in four different countries (Finland, Sweden, Canada, and the United States) speaks to the internationalization of the NHL and also the complex challenge it presents from a public health perspective. These players, given their varied childhood environments, may have received anywhere from 0 - 3 doses of a mumps-containing vaccine as different countries have varying requirements on mandating it.

With a vaccine-preventable disease, there are several angles that need to be considered. First and foremost is that of the players. One of the key aspects of the Code of Medical Ethics is that of patient autonomy - the idea that patients are allowed to make their own decisions with regards to treatment. From the American Medical Association’s website

“Respect for patient autonomy is central to professional ethics and physicians should involve patients in health care decisions commensurate with the patient’s decision-making capacity. Even when a medical condition or disorder impairs a patient’s decision-making capacity, the patient may still be able to participate in some aspects of decision making.”

Players were therefore allowed to make their own decisions, knowing the risks associated. Ryan Suter, who missed games with the mumps in the 2014-15 season had this to say:

“Everybody got the shots on our team, and I’m like ‘I don’t need to get the shot. I think I’ll be all right. I wash my hands a lot. I’m a clean guy,’” he said. “So everybody got it except for me. And of course, two weeks ago I get the mumps.”

However, how do we ensure players have “true” autonomy? Educating players is a fine balance between explaining the risks to them of not being vaccinated, and ensuring that they are not coerced into getting the vaccination, fearing reprisals from management or lost games (which could severely impact their career prospects, especially marginal/bubble players).

For owners, this becomes trickier. With players both being raised in and playing in leagues throughout the world, owners have to consider whether they want the same standard being applied across the board. For those who play in international competitions or are signed/drafted from international leagues, should they be encouraged to get their immunity checked as part of their physical evaluation? For owners, preventing their players from missing time, especially their star players, is a priority (as is evident from their hesitation to bring players to the Olympics). However, they may be reticent to encourage players to get vaccinated, risking repercussions from both the public and the players association.

The final angle is that of the league. While on some level this is synonymous with the owners, any change would have to be league-wide in order to ensure consistency and effective herd immunity among all players. The league has made changes that respect autonomy but also protect players, with issues such as visors being mandatory for newer players, but not for existing players, as well as the concussion protocol. While some may argue these do not go far enough, they show the league is willing and able to take action. After losing high profile players to (preventable) diseases, can the league afford to not take a stand?

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