Authorities are working hard to stop a major outbreak of syphilis and HIV in Milwaukee that has already gotten at least 125 people seriously ill. It is being described as one of the largest sexually transmitted infection clusters in United States history.

A dozen high school students are also included in that figure, according to the Milwaukee Journal Sentinel, and authorities expect the overall figure to grow as more people are discovered. Clinicians are trying to get ahead of the problem as best they can by asking about sexual history in order to identify potential new victims.

People between the ages of 15 and 24 appear to be most at risk in this situation, which affects the entire city and could have major consequences if authorities cannot figure it out soon. It appears to have affected infants in 2017 as well.

“Troubling publichealth news, there has been an increase in new cases of HIV/Syphilis. Sadly this included infants in 2017,” wrote the MKE Health Departmnet on Twitter recently. “On March 1st, MHD launched a commuter ad campaign with MCTS to raise awareness about sexually transmitted diseases.”