Health officials in Pima County are concerned that measles could spread across the state after nine people were diagnosed with the illness.
Since mid-February, four adults and four children have been infected after a 37-year-old woman visiting from Switzerland was diagnosed at Northwest Medical Center in Tucson, health officials said.
"They came into contact with her or others infected with the disease at the hospital or a doctor's office," said Dr. Karen Lewis, a medical director with the Arizona Department of Health Services.
Officials said it could have spread out of Pima County.
Just one case of the measles in a community is an outbreak, Lewis said. "You don't know how well people are immunized or not immunized until you have one case."
What has health officials concerned is a trend against vaccinating children, which Lewis said is born out of a belief in vaccine links to other problems, like autism.
Studies have shown no such link, Lewis said. "People have started to forget how bad of a disease it is and have started listening to people saying vaccines aren't good," Lewis said.
School age children in Arizona are required to get certain vaccinations before attending school, but parents can opt out of the requirement. None of the nine people infected by the disease in Pima County, who ranged in age from 11 months to 50 years, was immunized, Lewis said.
Measles is spread through the air, and people can become infected just by being in the same room or in a room with the same ventilation as someone infected.
Measles starts with a runny nose, high fever, cough, red eyes and an overall sick feeling, Lewis said. The fever is followed within a few days by a rash of red spots on the face and upper body. People experiencing those symptoms should notify their doctor's office or urgent-care facility before going in, so they don't potentially expose other people to the disease, she said.