Mumps — that old-timey viral infection causing swollen cheeks and jawlines — is making a strong comeback in Colorado in 2017, mirroring a national trend.

So far this year, 14 cases of mumps have been diagnosed in Colorado. Eleven of those cases in the Denver metro area are part of a linked outbreak that health officials are still sorting out, said Rachel Herlihy, the director of the Disease Control and Environmental Epidemiology Division at the Colorado Department of Public Health and Environment.

“We are actively investigating that outbreak and do expect those numbers to climb,” Herlihy said.

Colorado saw only 17 cases of mumps in all of 2016. Nationally, there were more than 5,300 cases in 2016, a massive increase over the previous five years when annual cases hovered around 1,000.

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September 1, 2020 Third virus vaccine reaches major hurdle: final U.S. testing Mumps was once common, and Herlihy said most people born before 1957 have probably been exposed to mumps in their lifetimes, meaning they are now likely immune. But vaccination drastically reduced the number of annual cases. People who are vaccinated can still catch mumps if exposed, but it is much less likely.

Herlihy said the latest outbreak in Colorado is among a mix of vaccinated and unvaccinated people.

Mumps spreads through direct contact with an infected person. It causes painful swelling in the glands of the cheek and jaw. More serious problems are possible but rare.