Seventy people have been infected in a measles outbreak that led California public health officials to urge those who haven't been vaccinated against the disease, including children too young to be immunized, should avoid Disney parks where the spread originated.

New infections linked to the theme parks emerged Wednesday in the outbreak that has spread to five U.S. states and Mexico, though the vast majority - 62 - occurred in California.

Because measles is highly contagious, people who have not received the measles-mumps-rubella, or MMR, vaccine are susceptible and should avoid visiting Disney "for the time being," state epidemiologist Gil Chavez said.

The same holds true for crowded places with a high concentration of international travelers, such as airports, Chavez said. People who are vaccinated don't need to take such precautions, he said.

Disneyland Resorts spokeswoman Suzi Brown said officials agreed with the advice that "it's absolutely safe to visit if you're vaccinated."

The people who have been infected range in age from 7 months to 70 years old. The vast majority were not vaccinated, and a quarter had to be hospitalized.

Among those sickened were five Disney employees. Three have since returned to work. The company previously said park employees who may have been in contact with those infected were asked to show proof of vaccination or have a blood test to show immunity against measles. Those with pending results were put on paid leave. Vaccinations are also being offered to all employees.

Measles has hit California hard recently. The state typically sees four to 60 measles cases a year.

"We are off to a bad start in 2015," Chavez said.

Since the outbreak, two dozen unvaccinated students at an Orange County high school were sent home for three weeks after an infected pupil showed up.

Measles is a highly contagious respiratory illness that can spread by air through coughing or sneezing. Symptoms include fever followed by cough, runny nose and a blotchy rash. Though the virus has been eradicated in the U.S. since 2000, it can still enter the country through an infected traveler.

While health officials said they likely may never find "patient zero" or the trigger of the outbreak, they believe it was either a resident from a country where measles is widespread or a Californian who went abroad and brought home the virus.

People at highest risk are those who are unvaccinated, pregnant women, infants under 6 months old, and those with weakened immune systems.