MILWAUKEE (CBS 58) — The Wisconsin Department of Health Services is reporting 92 measles cases associated with an outbreak in southwestern Wisconsin, more than double the 42 reported Tuesday.

"Wisconsin doesn't usually see outbreaks like this," Outreach Community Health Centers Chief Medical Officer Dr. Nicole Mubanga said. "It's very easy to make it catch on like wildfire."

DHS says the surge is tied to an ongoing outbreak in Grant, Iowa and Lafayette counties.

"It has been around for a really long time, but we're starting to see more and more of it because fewer people are getting vaccinated," Mubanga said.

Mubanga told CBS 58 that about 75% of 6-year-olds in Milwaukee have received both recommended doses of the measles, mumps and rubella vaccine.

"In order to get what we call herd immunity, or lower that risk of having a major outbreak, we need to see that number closer to 90%," Mubanga said.

As children return to the classroom, parents should keep an eye out for potential symptoms.

Measles symptoms can begin with a fever, runny nose, cough and red or watery eyes, followed several days later by a rash.

"I think there should always be a certain level of concern, but knowing that the cases are going up, it definitely is concerning," Mubanga said.

While children can be particularly vulnerable as they return to classrooms, adults can also become infected.

"If you are fully vaccinated, you've had your two shots, you're good to go. You're about 97% protected," Mubanga said.