Mumps Cases Surge in US as Outbreak at University of Missouri Climbs to 31 More than 2,940 mumps cases have been reported so far this year.

 -- Mumps outbreaks across the U.S. have sickened nearly 3,000 people, close to three times as many as in 2015, according to the U.S. Centers for Disease Control and Prevention.

At the University of Missouri, for example, a current outbreak has so far led to 31 confirmed cases of the disease and 27 other suspected cases.

Many other colleges and universities have grappled with mumps outbreaks this year, including Harvard, which in April reported having at least 40 confirmed cases.

The number of mumps cases in the U.S. can vary widely from year to year, ranging from a few hundred to a few thousand.

But 2016 has seen a particularly large rise, according to the CDC. More than 2,940 cases have been confirmed this year, up from the preliminary estimate of 1,057 for 2015. This year has also already surpassed the previous recent high 2,612 mumps cases in 2010.

After 2010, the number of infections fell significantly to 370 cases and stayed below 600 until climbing to over 1,000 cases in 2015, according to the CDC.

Colleges and universities have typically been at the center of many mumps outbreaks, Dr. William Schaffner, an infectious disease expert at Vanderbilt University Medical Center, told ABC News in a previous interview.

"Universities are a wonderful receptor site for young adults incubating mumps," he said.

Certain behaviors common at colleges and universities can help spread the virus, according to the CDC.

These include students being in a "crowded environment, such as attending the same class, playing on the same sports team, or living in a dormitory with a person who has mumps," the CDC said on its website. "Also, certain behaviors that result in exchanging saliva, such as kissing or sharing utensils, cups, lipstick or cigarettes, might increase spread of the virus."

Schaffner said that in the past some outbreaks have occurred when exchange students from European countries that do not have as robust vaccination programs as the U.S. arrive at a college already infected with mumps. Because the mumps vaccine isn’t 100-percent protective, an outbreak can then occur even among students who were vaccinated as children.

Mumps outbreaks in the U.S. “usually relate to mumps that is occurring in Europe,” said Schaffner. “I haven't seen the molecular data here, but that has certainly been a pattern in the past.”

Despite the increase in 2016, the number of mumps cases now is still a small fraction of what it was before a vaccination campaign started in 1967. At that time, around 186,000 cases of mumps were reported annually, according to the CDC.

The mumps vaccine is typically given to infants. The recommended two-dose vaccine course provides approximately 88 percent protection from infection and a single dose of vaccine provides 78 percent protection.