Valley measles outbreak grows: Where you may have been exposed

The Maricopa County Department of Public Health has identified 25 positive measles cases in the county since the start of the year, and on Tuesday announced a host of new exposure sites in Chandler and Phoenix. That comes on the heels of the department announcing exposure sites in Tempe and Surprise on Friday. The most recent exposures have been traced to a non-resident who tested positive for measles, the department said.

The department has not shared how many positive cases are children and whether any have suffered serious health effects. Measles is an incredibly contagious disease that can be especially dangerous to unvaccinated individuals, particularly very young children. Two doses of the measles-mumps-rubella vaccine are 97% effective at preventing the disease.

Twenty-five positive measles cases are the most the county has had since at least 2006, according to data from the Arizona Department of Health Services. Maricopa County had no cases last year and two in 2024. Before this year, the most the county has seen over the last 20 years was five cases in 2022.

In total, the state has seen 341 positive measles cases since the start of 2025, most of them concentrated in the Northern Arizona community of Colorado City, a former Fundamentalist Mormon stronghold where vaccination rates are very low. Ninety-five percent of cases have been in unvaccinated individuals, and 63% of positive cases have been minors. Twenty-five people have required hospitalization, but no one has died in the state due to measles.

The first exposure sites identified by county health officials were primarily in Gilbert and Queen Creek, with Mesa showing up among exposure sites in May. Exposures in Surprise, Phoenix, Tempe and Chandler have been more recent developments.