Epidemic salmonellosis from cheddar cheese: surveillance and prevention.

On August 3, 1976, ongoing Salmonella surveillance in Colorado first detected an epidemic of Salmonella heidelberg infections that eventually totaled 339 isolates. The majority of the cases occurred between July 23 and August 12 in two widely separated cities: Denver and Pueblo. Epidemiologic investigation successively incriminated 1) recent dining at Mexican-style restaurants (p less than 0.001), 2) eating foods containing cheese in these restaurants (p = 0.029), and 3) consumption of cheddar cheese from a single shipment of a single manufacturer (p less than 0.01). The prompt investigation enabled an embargo of 2087 kg (41%) of the contaminated cheese. S. heidelberg was isolated from seven production lots of the incriminated cheese. Surveillance and the epidemiologic investigation may have resulted in prevention of 25,000 diarrheal illnesses.