Perhaps the most surprising story of the first two months of the NHL season -- and possibly the strangest -- involves the mumps outbreak that has affected four teams and nine total players so far. But why? And why in the NHL?

Mumps is a viral disease that spreads through exposure to saliva from coughing, sneezing, or spitting and can infect different organs, most commonly the salivary glands inside the mouth. In infected patients, these glands become swollen and painful, and with the high fever, headache and loss of appetite that often comes along with the disease, the typical 7-to-14 day course can be miserable to experience. Since it's a viral illness, treatment typically consists of fever control, hydration and rest, without any specific cure.

Mumps was common in the United States before the mid-1960s, when a vaccine was developed that dropped the total number of cases to fewer than 1,000 per year. That said, the number of young adults who have become infected has risen in recent years, and there are several theories as to why.

For one, although mumps vaccinations are mandatory in the U.S., only three out of the 10 provinces in Canada require that children must be vaccinated. Second, although it is recommended that patients receive two vaccines (typically known as MMR: measles, mumps, and rubella) in childhood, at roughly 1 and 4 years of age, studies show that many patients miss the second "booster" shot, which is especially a problem given that approximately 22 percent of people do not develop measles immunity after only one dose of vaccine. And third, even among those who do receive both doses, more than 10 percent of patients will not develop immunity. So while the shot is effective, it is not foolproof.

Given these factors, and given the close quarters NHL players keep in locker rooms and on the ice, it isn't surprising that one player with the disease could potentially infect others who don't have immunity. And further, patients are contagious even before symptoms show up, so they might not even know they have the disease.

Going forward, the best thing teams can do -- other than use precautionary measures and keep individuals out of the locker rooms if experiencing symptoms -- is to re-vaccinate players on squads where there has been an outbreak. The New York Rangers, for one, did so after left wing Tanner Glass developed mumps, as likely have others. Otherwise, it stands to reason that as more teams are impacted by this outbreak, we'll continue to hear about more players needing to spend time in bed dealing with swollen salivary glands and high fevers throughout the winter.