Six new exposure sites in Phoenix and Chandler were tied to a measles-positive visitor who moved through the area on July 12-13, including Chase Field, Chandler Fashion Center and several restaurants.
Maricopa County's 2026 measles total has now reached 25 cases, far above its historical average of about one case a year over the past 30 years.
Health officials said measles can linger in the air for up to two hours after an infected person leaves, and unvaccinated people face a 90% chance of infection after exposure.
Symptoms usually appear 7 to 12 days after exposure, though they can take up to three weeks; residents at the listed sites were told to check vaccination records and monitor for fever, cough, red eyes and rash.
The county is urging MMR vaccination, including an early dose for infants 6 to 11 months, as a separate outbreak at a Florence ICE facility has already infected 7 detainees and disrupted operations.