Nine people who visited Southern California’s Disneyland or California Adventure theme parks during a five-day period in December have contracted measles, California health officials announced Wednesday.

Seven people have confirmed cases of measles in California, in addition to two confirmed cases in Utah, according to a California Department of Public Health release. Three more cases are being investigated in California. All visited either the Disneyland or California Adventure theme parks in Anaheim between December 15 and December 20.

“Based on information from current cases, it is likely that a person infectious with measles was at one of the theme parks on these dates,” the statement said. “The California confirmed cases reside in five local health jurisdictions (Alameda, Orange, Pasadena, Riverside, and San Diego) and range in age from 8 months to 21 years. Several large contact investigations are ongoing.”

In a statement, Walt Disney Parks and Resorts chief medical officer Dr. Pamela Hymel said the company is “working with the health department to provide any information and assistance we can.”

According to the health department, symptoms of measles include fever, cough, and a runny nose, with a red rash appearing after a few days. Measles is a “highly-infectious, airborne” infection, however the release notes that two doses of the MMR vaccine is more than 99 percent effective at prevention.

“If you have symptoms, and believe you may have been exposed, please contact your healthcare provider,” CDPH director Dr. Ron Chapman said in a statement. “The best way to prevent measles and its spread is to get vaccinated.”

Measles has reportedly been eliminated in the United States since 2000; however, the Los Angeles Times notes that there has been a recent increase in confirmed cases. Of the 62 confirmed cases of measles in California last year, 22 were reported in Orange County.