A report earlier this week of a couple of measles cases in Southwest Wisconsin has turned into an outbreak, with 13 more confirmed cases and six probable cases of the viral illness, the state health department reported Thursday.

The outbreak, in Iowa and Lafayette counties, highlights the importance of getting vaccinated for measles, considered the safest and most effective way to prevent the spread of the virus, said Dr. Ryan Westergaard, the chief medical officer in the communicable disease bureau of the Wisconsin Department of Health Services.

The new group of measles patients who have been diagnosed are in Iowa County, Westergaard told reporters at a DHS briefing on the findings. Most of them were not vaccinated for measles, he said.

DHS announced two measles cases Tuesday, one in Iowa County and one in Lafayette County, that were confirmed through tests at the Wisconsin State Lab of Hygiene. 

Those were the third and fourth measles cases in Wisconsin in 2026, and were not related to the first two this year, which were linked to out-of-state travel.

Subsequent investigation by the local public health departments in the two counties turned up the 13 confirmed and six suspected cases that DHS announced Thursday. None of the current cases have been tied to travel. 

“The rapid emergence of these cases, particularly among people who have not traveled outside of Wisconsin, indicates that there is active local transmission, and it’s very likely that additional cases exist in the community that have not yet been identified or reported to public health,” Westergaard said.

State tracks 23 cases so far

Westergaard said DHS would not release the ages or age range for any of the people with confirmed measles cases in the current outbreak in order to protect their privacy.

The department maintains a state registry for all measles cases that includes age ranges and vaccination status. Thursday evening, that record showed that of the 23 confirmed or suspected cases identified in Wisconsin in 2026, three were in children age 4 or younger, 11 were in children ages 5 to 17, and nine were in adults ages 18 or older.

Westergaard said that it’s likely that there are more people with measles whose cases haven’t been identified and therefore aren’t on the state’s dashboard.

With one exception, the patients identified in 2026 were not vaccinated for the measles virus, according to DHS. One has been hospitalized.

Vaccine is ‘single best tool’ to stop outbreaks

DHS is asking people to verify whether they’ve had the MMR vaccine — the shot that includes protection against measles, mumps and rubella. That information is probably available from a person’s regular health provider, if they have one, or from the Wisconsin immunization registry.

The MMR vaccine is usually given in a two-shot sequence: the first dose when a child is 12 to 15 months old, and the second when the child is 4 to 6 years old.

“Having received two doses of MMR vaccine provides exceptional, long-lasting protection, and this vaccine remains our single best tool to stop this and future outbreaks,” Westergaard said.

For an adult without a record of the shot or who is uncertain about having had it, it is safe to get an additional shot, he said.  

DHS is also asking people to be familiar with measles symptoms. Westergaard said those include a high fever, a red rash that starts at the head and spreads down and covers the whole body, a cough, a runny nose and red or bloodshot eyes.

A person who develops those symptoms, or whose family member experiences them, should call their regular healthcare provider, Westergaard said.

People with the symptoms should call ahead before visiting a clinic, urgent care or the emergency room, he said, so that medical personnel can take precautions to prevent airborne spread of the virus before a patient arrives to protect other patients in the facility’s waiting room.

Easily spread virus

“Measles is known to be one of the most contagious viruses,” Westergaard said, “and we treat every case very seriously, because our goal is to completely stop measles transmission in the community anytime we have a case or a cluster of cases.”

Measles can cause serious health problems, according to DHS — pneumonia, deafness, and brain damage as a result of swelling from the disease.

Local public health agencies in the two counties haven’t identified specific public places where the virus might have spread, Westergaard said.

One of the jobs of local public health departments is to track contagious illnesses such as measles in their communities or counties, he said. DHS supports local agencies as they work to trace who else has been exposed to the virus.

Trump urges shift in childhood vaccine recommendations, calls for splitting up MMR vaccine

When a person who’s been exposed has been identified, they’re monitored for symptoms “to make sure that if any new cases pop up, we can get them isolated right away,” Westergaard said.

While the current outbreak is still small, “it’s a dynamic situation,” he added. With help from DHS, local health departments are tracing the spread of the virus and watching for more people who develop symptoms, “because that would be a sign that it’s getting larger.”

New Trump order ‘contradicts the best available science’

Thursday’s announcement follows an order Monday from President Donald Trump. Wisconsin’s top health official said Thursday that Trump’s order goes against the best scientific recommendations for measles prevention.

Trump’s order calls for separating the MMR vaccine into separate shots for each illness.

“There is no new scientific evidence that justifies changing recommendations that have, and continue to, protect children across the United States,” said Kirsten Johnson, secretary-designee of Wisconsin DHS, in a statement released Thursday.

“The executive order does not square at all with our recommendations on how to prevent measles or other vaccine-preventable diseases,” Westergaard said. “It was not science-based. It actually contradicts the best available science about how to prevent disease and keep kids healthy.”

DHS early this year turned from the Trump administration’s Centers for Disease Control and Prevention’s vaccine recommendations after the agency cast aside previous longstanding vaccine guidance.

DHS instead has endorsed the childhood vaccine recommendations from the American Academy of Pediatrics and the American Academy of Family Physicians.  

Westergaard said vaccinations in Wisconsin have fallen below the 95% rate that helps ensure widespread protection from illnesses that vaccines can prevent, and are even below 90%. That has happened for many complex reasons, he said — including misinformation, sometimes spread deliberately.

Wisconsin has so far avoided the “massive outbreaks” of measles that have occurred in states such as Utah, Texas and North Carolina, Westergaard said. Public health officials can contain the illness if they learn early of cases and are able to move quickly to identify and quarantine patients. But that’s more challenging because the state’s vaccination rate is lower than it should be, he said.

In addition to encouraging more vaccination, cooperation with public health measures is “a second layer of defense,” Westergaard said. “Let’s work together as a community, as a team, when an outbreak happens — be willing to share information, be willing to stay home when any symptoms happen, and allow us to identify the extent of an outbreak and to stop it.”