Frequency of Salmonella typhimurium the year after a massive outbreak.

In 1985, Illinois experienced a large milkborne outbreak of Salmonella typhimurium with over 16,000 cases. During this year, 49.4% of United States and 86.4% of Illinois salmonellae were S. typhimurium. In 1986, 1133 microbiologically confirmed and serotyped cases of salmonellosis were reported in the City of Chicago, comprising 37% of the 3034 cases reported for the State of Illinois. The most frequent serotypes were S. typhimurium (21.3%), Salmonella heidelberg (18.2%), Salmonella enteritidis (10.7%), and Salmonella braenderup (7.7%), similar to the state as a whole. Nationally, excluding Illinois, the most frequent serotypes in 1986 were S. typhimurium (26.1%), S. enteritidis (14.7%), and S. heidelberg (13.0%). S. braenderup comprised 0.9% of the non-Illinois total. Regional variations in the epidemiology of salmonellae are probable and may reflect detected or undetected outbreaks. Within a year of the nation's largest Salmonella outbreak, there was no trace of any effect on the frequency of isolation of Salmonella spp.