A measles outbreak that started in Disney’s (DIS) Disneyland amusement park in Calif., is spreading outside of the park.

The measles outbreak in the state has spread to 59 people. At least 42 of these people have had their infections linked to Disneyland. It’s unknown if the outbreak started at the Disneyland or Disney California Adventure Park, both of which are in the same city, reports Newsweek.

The measles outbreak is believed to have started around December 15, 2014. Among those infected by the initial outbreak were five employees working at the parks. The outbreak has been declared the worst measles infection that California has seen in 15 years, Newsweek notes.

“We can expect to see many more cases of this vaccine-preventable disease unless people take precautionary measures,” Dr. Gil Chavez, the deputy director for the Center for Infectious Diseases with the California Department of Public Health, told SFGate. “I am asking unvaccinated Californians to consider getting immunized to protect themselves and family and community at large.”

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