Molecular epidemiology of Salmonella typhimurium isolates from human sporadic and outbreak cases.

The molecular epidemiology of a representative collection of sporadic foreign and domestically acquired Salmonella Typhimurium (S. Typhimurium) isolates from Norwegian patients in 1996-9 was studied by numerical analysis of pulsed-field gel electrophoresis (PFGE) profiles. Three subclusters (E5, F1 and G1) comprised 47% of the 102 sporadic isolates investigated and 45% of the domestically acquired isolates fell in subclusters E5 and F1. Distinct seasonal and geographic variations were evident for these strains which have been responsible for both local outbreaks (E5) and a national epidemic (F1) where salmonella-infected hedgehogs and birds constituted the suggested primary source of infection. Subcluster G1 was dominated by imported multi-resistant definitive type (DT) 104 isolates. All multi-resistant isolates contained integron-associated gene cassette-structures. This study presents valuable information on the relative significance, geographic distribution and antibiotic resistance features of distinct S. Typhimurium clones causing human salmonellosis among Norwegians.