Arizona is in the midst of the largest current measles outbreak in the U.S. — and health officials are blaming unvaccinated workers at a federal immigration facility.

Officials have confirmed 22 cases of measles in the state since late May, and they all can be traced back to the Eloy detention center, a privately managed Immigration and Customs Enforcement (ICE) facility, reported the Associated Press.

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The Pinal County health director said the outbreak probably started with a migrant, but all the detainees have since been vaccinated.

However, the health director said, some employees of the facility managed by Corrections Corporation of America have refused to get vaccinated or show proof of immunity.

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ICE doesn’t publicly release its staffing levels, but health director Thomas Schryer believes the agency employs about 100 workers alongside 350 CCA employees at the Eloy facility.

“They’re actually the ones that are passing along the measles among each other and then going out into the community,” Schryer said.

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About 1,200 detainees are currently held at the facility.

An ICE spokeswoman said the agency had provided immunizations, referred staffers to nearby clinics, handed out pamphlets on the dangers of measles, and provided masks and gloves to help prevent spread of the disease.

The Tennessee-based CCA said most of its staffers had been vaccinated or shown proof of immunity, and the others are required to wear surgical masks or stay home.

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The Arizona health department director said the facility’s operators had been more responsive to the outbreak in the last week, and a large number of CCA workers were recently vaccinated.

Arizona has sent physicians into the detention center to share information with and offer free immunizations to workers who are reluctant to be vaccinated, and health officials may ask the governor to declare a state of emergency.

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Measles is highly contagious but preventable through vaccines, although health officials say many Americans resist immunization because they underestimate the danger from the disease.

It was eradicated in the U.S. in 2000, but new cases have been reported in recent years after a since-discredited study linked vaccines to autism.

Watch this video report posted online by KPNX-TV: