“This case is especially concerning because the source of the patient’s infection is unknown,” said Dorothy Adams, executive director of the Salt Lake County Health Department. “They have not knowingly had contact with anyone who had measles, which means their infection is the result of transmission somewhere out in the community.”

The county warned that anyone who went to Intermountain Health’s Taylorsville urgent care clinic on Nov. 7 from 3 p.m. to 7:15 p.m. may have been exposed. The virus is highly contagious and can linger in the air for up to two hours, so it doesn’t need direct contact to spread.

With that in mind, health department employees were getting in touch with people who might have been in close contact with the patient or visited the same spaces within a few hours.

The department first learned Wednesday night that someone tested positive. Citing patient privacy reasons, it did not give the patient’s age or gender, or say where the person lives.

On Oct. 27, the county announced a likely case based on the symptoms of a patient who refused testing. The last time the county recorded a positive test was in 2023, when a Utah resident got infected while traveling out of state, said spokesperson Gabriel Moreno.

Outbreaks happened earlier this year in rural parts of the state, including along the Utah-Arizona border and in Cache County.

Two doses of the measles, mumps and rubella vaccine prevent more than 97% of infections, the health department said, and those who are vaccinated and still get sick tend to have milder symptoms. Unvaccinated people — including babies too young to be eligible and immune-compromised Utahns — are more likely to experience severe complications.

Symptoms include fever, cough, runny nose and red or watery eyes, followed by a rash that typically begins days later on the head or face.

For those who don’t know if they’re immune, the county said receiving an additional dose of the MMR vaccine is safe and widely available, including at its vaccine clinics.