On Apr. 12, 1985, the U.S. Centers for Disease Control and Prevention (CDC) announced that between March 22, and April 8, 1985, over 1,500 culture-confirmed cases of salmonellosis in northern Illinois have been reported to the Illinois Department of Public Health.

Investigations linked the outbreak to 2% pasteurized milk (“Blue Brook” brand) from one processing plant. Salmonella typhimurium, resistant to ampicillin and tetracycline, was isolated from patients and from milk in unopened cartons.

The dairy stopped producing milk April 9, and investigations by local, state, and federal officials were ongoing.

Pasteurized milk constitutes approximately 99% of all (cow) milk consumed in the United States, but milk-borne outbreaks of Salmonella investigated by CDC in the past have almost always involved raw milk because effective pasteurization kills Salmonella.

The large number of affected persons in this outbreak illustrates how a widely consumed product, once contaminated, can result in many cases. Similar widespread transmission of Salmonella occurred in a waterborne outbreak involving an estimated 16,000 people (100 reported cases) in Riverside, California, in 1965 and in an estimated 3,400 affected Navajo Indians (105 investigated cases) at a barbecue on a reservation in 1974.