An investigation into an outbreak of Salmonella Typhimurium among patrons of Portillo's Restaurant in St. Charles, Illinois, was first announced on May 10, 2011. Cases were infected with a rare strain of Salmonella Typhimurium. There were 36 case patients meeting the case definition of which 19 were laboratory confirmed with S. Typhimurium. Cases resided in Kane, DuPage, Cook, DeKalb, Kenall and Will Counties. Two case patients lived in Minnesota but traveled to St. Charles in Kane County. An investigation was conducted by the Illinois Department of Public Health and the Kane County Health Department. Investigators concluded that a salad prepared at Portillos was the contaminated food item. They did not determine how the salad became contaminated with Salmonella.