Molecular epidemiology of an outbreak caused by Salmonella enterica serovar Newport in Finland and the United Kingdom

Between December 1997 and January 1998 an increase in the number of isolate s of Salmonella enterica serovar Newport, a serotype rarely causing indigen ous infections in Finland, was detected. This included two clusters of gast roenteritis following funeral meals. An inquiry via Enter-net revealed a co ncomitant increase in cases of S. Newport in the United Kingdom. To investi gate the Finnish outbreak, a total of 56 S. Newport strains (22 from the ou tbreak period, 27 from pre- and post-outbreak period, and 7 from imported f ood producing animals) were studied by pulsed-field gel electrophoresis (PF GE); selected isolates were also phage typed. Two retrospective questionnai re studies evaluating food exposures among the funeral attendants were cond ucted. All isolates from the clusters had an identical PFGE pattern which w as also found in 13 infections temporally close to but not associated with the clusters. The Finnish outbreak was caused by the same phage type as the one in the United Kingdom. In both clusters, an epidemiological link betwe en illness and exposure to cured ham was found. In conclusion, the outbreak was not limited to the two clusters but was more widely spread both in and outside Finland. Early alarm systems of food-borne outbreaks and collabora tion between European countries are needed for investigating international outbreaks.