[Extraintestinal Salmonella infections in four Danish counties. Inverse relationship between invasiveness and...

The relationship between invasiveness and incidence of non-typhoid salmonellosis was ascertained retrospectively in a population of 1.9 million in four Danish counties during the three-year period 1992-1994. The study comprised 4175 cases diagnosed by culture either locally or at Statens Serum Institut, Copenhagen. Two hundred and forty-four patients had extraintestinal infections caused by 24 out of the total number of 101 different serotypes. Invasiveness ranged widely from 4% to > 90% for individual serotypes. Salmonella typhimurium and Salmonella enteritidis formed a high-incidence group (incidence rates > or = 25/100,000/year) compared to the remaining 22 serotypes (< 5/100,000/year). The low-incidence group was more invasive than the high-incidence group even when excluding Salmonella dublin, which is highly invasive, and including 212 cases of salmonelloses caused by serotypes isolated entirely from faeces (relative risk 1.54, 95% confidence limits 1.19 < RR < 2.00). The data corroborate a previous more limited study and indicate that previous exposure to salmonella and acquired immunity may play a role in the occurrence of extraintestinal non-typhoid salmonellosis.