A spokesman for the California state health department has told Reuters that he believes “unvaccinated individuals have been the principal factor” in a mid-December measles outbreak at Disneyland that has infected more than 70 people in six western states and Mexico, including five Disney employees.

The outbreak of the respiratory disease, which is caused by a highly communicable virus, has increased the focus on parents who choose not to vaccinate their children. Measles was thought to have been eliminated in the United States in 2000, meaning the disease is not native to the U.S. (Nonetheless, 644 measles cases were reported in America in 2014.) But it is not uncommon in the rest of the world, and healthcare officials presume an infected foreigner brought the virus to Disneyland or the accompanying Disneyland Adventure Theme Park in Anaheim, Calif., between Dec. 15 and 20.

Of the 34 California measles victims whose vaccination history could be ascertained, 28 had not received the measles shot. The American Academy of Pediatrics and the Centers for Disease Control recommend that children first receive the MMR (Measles, Mumps, Rubella) vaccine at the age of 12-15 months and then again between their fourth and sixth birthdays.

[Reuters]

Write to Jack Dickey at jack.dickey@time.com.