The measles outbreak reported earlier this month in Southwest Wisconsin has increased markedly this week, the state health department reported Friday.

With newly identified cases, the total number of people in Grant, Iowa and Lafayette counties confirmed with the viral illness has increased to 92, according to the Wisconsin Department of Health Services. Another six people have been identified as probably having measles.

In addition to those 98 patients, two other people in Wisconsin were diagnosed with measles at the beginning of 2026. All but one of the 100 Wisconsinites with confirmed or probable measles this year had not been vaccinated, according to DHS.

Of all Wisconsin measles patients this year, 40% are 18 years old or older, 46% are 5 to 17 years old and 14% are age 4 or younger, according to DHS. The department doesn’t publish the demographic information for specific outbreaks.

So far the Southwest Wisconsin outbreak has not been spreading through general public exposure, according to DHS.

“There’s ongoing transmission of disease from previously identified cases,” said Dr. Stephanie Schauer, DHS immunization program manager, in a video recorded by the department Friday. “So this speaks to the very infectious nature of measles.”

Nine out of 10 people who are susceptible to measles and exposed to someone with the virus, such as a family member or a person they live with, will come down with the illness, she said.

“So if one person in that household becomes sick with measles, and then they expose others in that household, those others are likely to become sick about 10 to 14 days later,” Schauer said.

The measles vaccine — typically delivered in combination with mumps and rubella vaccines — remains the best prevention from the virus, Schauer said.

Earlier this week the Centers for Disease Control reported 2,777 measles cases nationwide. The first two deaths from measles in the U.S. this year were confirmed this week in Pennsylvania, the Pennsylvania Capital-Star reported.

An outbreak of measles in two counties reported earlier this month has spread and is affecting 48 people, the state health department reported Friday.

The Wisconsin Department of Health Services has identified a total of 41 confirmed cases and seven “probable” cases, reported in Grant, Iowa and Lafayette counties. They include two cases in Grant County, which were reported earlier this week, and 35 in Iowa County.

In Lafayette County, the count is now four confirmed measles cases and seven probable cases. One of the confirmed cases is new, along with the four probable cases, DHS reported in an updated announcement. 

So far DHS has not found evidence of public exposure to the virus, meaning the cases identified so far appear to have been spread between people who knew each other.

State health officials are recommending that people check their vaccination status. The MMR (measles, mumps and rubella) vaccine is the best protection against measles, health officials say.

DHS is recommending that anyone who isn’t sure whether they have the MMR vaccine check their vaccination status at the Wisconsin Immunization Registry or with their local public health department or healthcare provider.

A federal report in July found that nationwide, measles cases have reached their highest level in 35 years. The reemergence of the viral illness, which public health experts said had been eliminated by 2000, coincides with declining vaccination rates in the U.S.

Since Jan. 1, the number of Wisconsin measles cases has grown to 50, according to DHS, and with one exception, everyone who has taken ill was not vaccinated for the disease. 

DHS operates a Measles Dashboard and a webpage for Outbreaks and Investigations that supplies more public information about public health conditions, with 12% of cases in children age 4 or younger, 44% in children ages 5 to 17, and 44% in adults 18 or older.

This report was updated with additional information from DHS.