TUCSON, Ariz. >> Health officials in Arizona say the largest current measles outbreak in the United States is in part because some workers at a federal immigration detention center refuse to get vaccinated.

Authorities have confirmed 22 measles cases in Arizona since late May. They all stem from the Eloy Detention Center, an Immigration and Customs Enforcement facility managed by the Corrections Corporation of America.

Pinal County health director Thomas Schryer says the outbreak likely began with a migrant but that detainees have since been vaccinated.

He said ICE employees at the large facility have not been as cooperative. Nine of the 22 total cases were facility staff.

ICE says the agency is working closely with health officials to monitor detainees and employees. CCA says most of its workers have gotten immunized or are wearing surgical masks while looking for proof of immunity.