The number of reported measles cases in California has grown to at least 73, with 50 of them linked to the Disney theme park outbreak, state health officials said.
An addition 15 measles cases were reported in Arizona, Illinois, Utah, Washington, Colorado, Oregon, Nebraska and Mexico.
Two additional cases were confirmed in Ventura County on Tuesday, bringing the total number of cases there to eight, according to county health spokeswoman Sheila Murphy.
Doctors believe the person who triggered the outbreak visited Disneyland sometime between Dec. 15 and Dec. 20.
Top news of the day
Most of the people who were infected were not vaccinated, according to the Associated Press.
More than 95 percent of people who receive the MMR vaccination will develop immunity to measles, mumps and rubella, according to the Centers for Disease Control and Prevention.
A record number of measles cases were reported in the U.S. last year, with 644 total infections reported in 27 states.
Measles is an airborne disease that is spread through sneezing or coughing. Widespread use of the vaccine has dramatically reduced the number of reported cases each year. Three to four million Americans were infected each year in the decade before the measles vaccination program began, according to the CDC.
The Associated Press contributed to this report.