Survey of extraintestinal nontyphoid Salmonella infections in a Danish region. Inverse relation of invasiveness to frequency of isolation.

A total of 790 cases of nontyphoid salmonellosis distributed among 44 serotypes was registered in the County of Northern Jutland, Denmark (population 487,000) during a 3-year period from January 1992 to December 1994. There were 45 cases of extraintestinal infection, 30 of which had a positive blood culture, 12 a positive urine culture, and 5 a positive culture of either pus or tissue. For the 9 serotypes represented by > or = 5 isolates the proportion of extraintestinal isolates was inversely related to overall frequency of isolation (chi-square test, f = 1, p = 0.00003). Although limited, our study is consistent with surveys in the UK and US pointing to a modifying effect of exposure on the invasiveness of nontyphoid Salmonella serotypes.