State health officials say the number of confirmed cases of mumps at Keystone Ski Resort has risen to 26.

The Summit Daily News reports that as of Thursday, two dozen of those infected at Keystone are employees and two are non-employees. The outbreak began on Feb. 2 with three cases reported.

Summit County Public Health officials say the risk of infection is limited to people who come in close physical contact with someone who is infected. Officials are investigating how the non-employees were infected.

Last year, there was a total of 67 mumps cases in all of Colorado.

Mumps is a contagious viral disease that causes pain and swelling in the salivary glands.