Drastic changes in the number of the cases of mumps reported each year to the Centers for Disease Control and Prevention demonstrates how the incidence of mumps fluctuates depending on the number of outbreaks. This year outbreaks of mumps have surfaced at several colleges and universities, where crowded dormitories occasionally incubate clusters of the disease. Mumps is still rare: A double dose of the Measles, Mumps and Rubella (MMR) vaccine in early childhood is 88 percent effective at protecting against the virus, according to the CDC.

A student was diagnosed with mumps at San Diego State University last week, bringing the total number of cases in the San Diego region this year to an usually high 19. San Diego averaged two cases of mumps per year from 2011 to 2014, according to the most recent data from the California Department of Health and Human Services. Cases have also been reported this year at California State San Marcos and San Diego Christian College.

This graphic may underreport the true number of cases, as the CDC does not require that every outbreak be reported to the centers.