The 1985 California listeria outbreak was in Mexican style soft cheese made by Jalisco in California. There were 52 confirmed deaths, including 19 stillbirths and 10 infant deaths. At the time, it was the deadliest foodborne illness outbreak in the United States, measured by the number of deaths, since the Centers for Disease Control and Prevention had begun tracking outbreaks in the 1970s.
1985 California listeriosis outbreak in cheese Wikipedia
Alta Dena supplied the raw milk to Jalisco to make the soft Mexican-style cheese in 1985. Jalisco had a non-licensed technician perform the pasteurization. Pasteurized milk might have been diluted with non-pasteurized milk by the technician.
The cheese caused 142 cases of listeriosis in 1985, including 52 fatalities.
On July 15, 1989 Alta Dena was absolved of any blame.