Updated: 2:13 p.m.

Another measles outbreak in Oregon is bringing the total number of cases reported in the state this year to 23, the most since 1991, according to a news release from Multnomah County.

The outbreak reported today is the third in Oregon this year and involves nine cases in Clackamas and Multnomah counties confirmed since the beginning of July.

None of the nine people who came down with measles was immunized, according to health officials. Eight of the people who contracted the disease were under 18, officials said.

“We cannot pinpoint exactly when this outbreak started,” Multnomah County Deputy Health Officer Dr. Jennifer Vines said. “A local resident had a measles-like illness in early July. Since then the additional cases have been limited to close contacts who were unvaccinated. Those individuals have been in close touch with public health during symptom watch.”

Unlike in some other outbreaks, all the nine people who contracted the disease have stayed at home while they are contagious, the release said, which means they haven’t posed any risk to the public.

With the school year set to start for many Oregon students in the coming weeks, health officials are asking parents to make sure their kids are fully immunized.

“Measles is a serious illness, people are miserable for a week and very contagious while sick,” Vines said in the release. “The vaccine is safe and effective; it keeps kids healthy and in school. Fully vaccinated kids also protect their siblings, friends and teachers.”

Information on measles in the state provided by the Oregon Health Authority shows that Oregon suffered through several years of high numbers of measles from 1989 to 1991. In 1991, the state identified 100 measles cases.

Symptoms of measles include a runny nose, cough, and a high fever followed by a whole-body rash, health officials said. The disease can also have more serious complications, the Multnomah County news release said, including “permanent hearing loss, blindness, pneumonia, and life-threatening brain infection.”

“A measles case in school can be dangerous to unvaccinated pregnant women and medically fragile children and adults,” Vines said, adding that students who are unvaccinated and exposed to measles must stay out school for 21 days.

“That means missing sports, parties and class time,” she said. “And that may be a burden on working parents who have to find childcare.”