In September 2023, the McHenry County Department of Health investigated an outbreak of E. coli O157:H7 infections among students and staff at Huntley High School. In total, 16 outbreak associated cases were identified. Dates of illness onset ranged primarily from September 10 to September 15. One case, considered to be a secondary case, became ill on September 18. All 15 primary cases ate at the school cafeteria and all 15 ate a sandwich from the cold sandwich station.

An asymptomatic food handler that worked at the cold sandwich station, providing garnishes (lettuce and cheese) to the sandwiches was positive for Shiga Toxin E. coli by PCR although this finding could not be confirmed by culture. Repeated testing revealed the food handler was most likely shedding STEC intermittently. Investigators theorized the food handler was the source of the outbreak.