SUMMARYThis report summarizes studies on 1699 foodborne outbreaks, in Italy, reported to the Istituto Superiore di Sanitai (ISS) (the National Institute of Health of Italy, Rome) during the period 1991-4. The most frequently reported foodborne outbreaks were caused by salmonellae (81 %), in particular by Salmonella enteritidis and non-serotyped group D salmonella (34% and 33 % of the total salmonella outbreaks, respectively). A vehicle was implicated in 69 % of the salmonella outbreaks; eggs were implicated in 77 % of the outbreaks for which a vehicle was identified or suspected. Salmonella strains isolated in 54 outbreaks were studied for phenotypic and genotypic characteristics. The isolates belonged to S. enteritidis (50 outbreaks), S. typhimurium (three outbreaks) and S. hadar (one outbreak). In the S. enteritidis outbreaks, phage type 4 was most frequently isolated (64-8 %), followed by phage type 1 (14-8 %). The virulence plasmid of 38 megadaltons was found in many different phage types of S. enteritidis.

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Seventeen strains of Yersinia enterocolitica biotype 4 serotype 03 were isolated from 63 apparently healthy puppies. Of these strains, 76.4% showed both multiple resistance to antimicrobial agents and lack of sorbose fermentation.

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In September 1994 an outbreak of gastroenteritis occurred in 437 people who had consumed lunch in the canteen of a factory in Central Italy. Salmonella sp. was isolated from stools of 99 patients and in 73 of them Salmonella hadar was identified. This is the first outbreak caused by this serotype described in Italy. In order to examine the genotypic basis of the epidemic strains, molecular typing was applied to sporadic strains isolated before and after the outbreak episode. For this purpose phage type, resistance to antibiotics, DNA plasmid profile and sites of insertion of the mobile element of IS200 were determined. The epidemic strains were genetically distinct from the non‐epidemic isolates; they were shown to be phage type 26, harbouring four small plasmids, were resistant to nalidixic acid and showed a unique characteristic IS200 fingerprint. The typing methods used in this study allowed the identification and discrimination of the outbreak strains from related isolates. They can thus be considered as a tool for epidemiological purposes. In addition we should point out the emerging resistance to nalidixic acid, largely used in veterinary medicine, in Salm. hadar.