A measles outbreak linked to Disneyland continues to spread and while California remains the hardest hit state, health officials in Arizona are on high alert ahead of the Super Bowl.

Authorities have confirmed at least 109 cases, 91 of which are in California, according to a Friday update from the California Department of Public Health. That’s up from 78 cases reported on Jan. 23. Seven Arizona residents have been infected, but at least 1,000 people in three counties in the Grand Canyon state have also been exposed to the highly contagious airborne disease,

“This is a critical point in this outbreak,” the director of Arizona Department of Health Services, Will Humble, wrote in a blog post.

“If the public health system and medical community are able to identify every single susceptible case and get them into isolation, we have a chance of stopping this outbreak here,” he said. “However, if we miss any potential cases and some of them go to a congregate setting with numerous susceptible contacts, we could be in for a long and protracted outbreak.”

And the so-called critical point comes as droves of people travel to the Greater Phoenix area to attend the Super Bowl on Sunday. Health officials have warned that any unvaccinated person—including children— should stay home for three weeks and are urging the sick to stay away from places where large amounts of people congregate.

The 1,000 people who have been exposed to measles have been connected to three counties, Pinal, Maricopa and Gila. Glendale, where the Super Bowl is taking place, is in Maricopa County. Although Arizona officials admittedly have a laser-focus on the outbreak, one cautioned that people shouldn’t panic.

“If you go out in public, you are way more likely to get the flu. What we’re trying to do is nip this in the bud, track people who’ve been exposed, keep them out of child care and work, so it doesn’t become widespread,” Maricopa County Public Health Director Bob England told USA Today.

In California in recent days, the measles outbreak has spread to another Northern California county, Marin, according to the California Department of Public Health. The two Marin cases were unvaccinated.

Health officials believe an international traveler brought measles to Disneyland, but the outbreak has led many to point the finger at parents who choose not to vaccinate their children because they believe it causes autism, a scientifically disputed claim. Two doses of the measles vaccine, known as MMR, are 99% effective in preventing illness, although one must be at least a year old for the first dose.

Some California schools have ordered students who are not vaccinated to stay home until they show proof of immunization or resistance to the virus. In Riverside County, 66 unvaccinated students were banned from school, according to The Los Angeles Times. In Orange County, at least 24 students were told to stay home for 21 days after a Huntington Beach High School student became infected.

Orange County, where Disneyland is located, has the most confirmed cases of measles, 27, followed by neighboring Los Angeles. Other cases connected to the Disneyland outbreak have also been confirmed in Utah, Nebraska, Michigan, Washington, Oregon Colorado and Mexico.

The virus was all but eradicated from the U.S. in 2000, but outbreaks abroad are common. People with measles suffer from fever, cough, runny nose, pink eye and a rash.

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