That's when the disease will have run its course, assuming no new cases pop up.
Because measles is so contagious 90 percent of people who come into contact with an infected person will develop measles if they haven't been immunized one case makes it an outbreak.
"Measles remains a significant infectious disease," said Gary Edwards, the health department's executive director. "We take significant efforts whenever there is a measles case."
The health department did not disclose the age of the measles patient or his school. But the school posted a notice on its website.
The health department's efforts include trying to track down where the teen got the measles, contacting anyone the teen came in contact with while he was contagious, and telling hospitals and doctors to be on the lookout for patients with measles symptoms.
Measles is passed in respiratory droplets from coughing or sneezing or direct contact with secretions of the infected person.
Measles symptoms start about 10 days after exposure and initially resemble a cold, including a cough, fever of 101 degrees or greater, runny nose and red, watery eyes. A rash starts a few days later and typically spreads from the face to all over the body. An infected person is contagious three to five days before the rash appears and at least four days after.
About 30 percent of people with measles will develop complications, said Dagmar Vitek, the health department's medical director.
According to the Centers for Disease Control and Prevention, 10 percent of children with measles will develop an ear infection; one in 20 gets pneumonia. And for every 1,000 children who get measles, up to three will die.
"It's a very, very concerning disease," Vitek said.
The health department believes the teen contracted the measles from someone in the state because he hadn't traveled, meaning there are at least two cases in Utah.
"Obviously, there's someone else out there," Vitek said.
The initial case was likely a foreign-born person, Vitek said, because most of the measles cases in the United States have been "imported" from Africa, Europe and Asia.
She said she couldn't predict if the outbreak would spread it will depend on whether or not the people who were exposed to the teen and the initial case were immunized. That's something the health department is trying to track down.
The health department will also contact the Olympus High students who have not been immunized to educate them about the disease and to see if they develop measles, Vitek said.
The teen had not been immunized, according to the health department. He had sought treatment in an emergency room. Measles cases must be reported by hospitals and physicians to the health department.
Most school-age children in Utah 97 percent have received two doses of the measles, mumps, rubella vaccine, according to the state health department. Parents can exempt their children from vaccinations for medical, religious or personal reasons.
Children under age one, who cannot be immunized, remain vulnerable, Vitek noted. So do older adults.
Health officials recommend that children receive two doses of the measles vaccine, the first by 15 months and the second before they start school at 4 to 6 years old.
"Whoever is not immunized, please do get immunized," Vitek said.
She said people who have been exposed can still get vaccinated within a short window of time and avoid the disease.
Horsley, with the Granite school district, said the school may offer vaccinations to staffers Friday.
But school will otherwise continue as scheduled, Horsley said. He said parents have no reason to be concerned about sending their children to school as long as they've received the immunizations.
The district contacted Olympus parents Thursday, via its phone system, to notify them about the measles case. It also posted a letter from the health department on the Olympus High website.
"There's really no reason for us to cancel school when they're only going to be missing around 30 students," he said.