Investigations related to the epidemic strain involved in the French listeriosis outbreak in 1992.

Two hundred seventy-nine cases of human listeriosis (92 pregnancy-related cases and 187 non-pregnancy-related cases) caused by a serovar 4b and phagovar 2389:2425:3274:2671:47:108:340 strain were identified in France between March and December 1992. Epidemiological investigations included a case-control study (not described here) and microbiological analyses of foods. Results of the case-control study and characterization of food isolates identified pork tongue in jelly, a ready-to-eat meat product, as the major vehicle of this outbreak, and to a lesser extent, delicatessen products contaminated secondarily during handling in food stores. As far as serotyping, phage typing, DNA macrorestriction pattern analysis (obtained by pulsed-field gel electrophoresis [PFGE]), and ribotyping are concerned, this epidemic strain is phenotypically and genomically closely related to strains responsible for major outbreaks of listeriosis previously observed in Europe and North America. The epidemic strain sensu stricto as defined by PFGE (2/1/3) displayed the same serovar, phagovar, ribovar, and ApaI and NotI PFGE patterns as the epidemic strains from outbreaks in Switzerland, California, and Denmark, but it consistently showed differences in the SmaI PFGE profile. This information greatly contributed to the identification of the major food vehicle (pork tongue in jelly) and further allowed exclusion of other foods (cheese) as possible sources of this major listeriosis epidemic.