Wisconsin health officials are investigating five probable measles cases in Rock County, the state Department of Health Services and Rock County Public Health said Oct. 13, 2026. The cases are connected to one another but are not linked to an ongoing measles outbreak in southwest Wisconsin. The Rock County cases are considered probable based on symptoms; laboratory testing has not confirmed them, and the source of infection is unknown. Officials said they have identified people who may have been exposed and are contacting them directly. No public exposure notice is currently needed. If investigators find a potential exposure site and cannot reach everyone who may have been there, they may share the location publicly. Since August, confirmed measles cases have been reported in Chippewa, Grant, Iowa, Lafayette, Marathon and Vernon counties. Wisconsin has recorded 267 confirmed cases statewide this year, according to the health department. Measles spreads through the air and can remain in the air for up to two hours after an infected person coughs or sneezes. The illness can lead to serious complications, including pneumonia, brain damage and deafness, and can sometimes be fatal.