Investigation of an outbreak of Salmonella enterica subsp. enterica serovar Hadar food illness in the Abruzzi region of Italy.

A comparative study was made of 22 strains of Salmonella Hadar isolated from victims of an outbreak of food illness in the Abruzzi region of Italy in 2000 and 21 strains of the same serotype isolated from poultry meat and human stool samples in the Abruzzi and Molise regions between 2000 and 2001. The aim of the investigation was to provide an epidemiological interpretation of the food illness outbreak to establish the degree of similarity between the S. Hadar strains isolated from victims of the outbreak and those isolated from poultry meat (identified but unconfirmed as the possible source of infection) and from other human samples received in the laboratory. Pulsed-field gel electrophoresis (PFGE) and random amplified polymorphic DNA (RAPD) were used to identify the genotypes and antimicrobial resistance patterns were determined. PFGE analysis of the restriction patterns obtained with XbaI and BlnI led to the identification of 12 pulsotypes in three groups. RAPD did not provide any information, as it was unable to differentiate between the strains isolated from food illness victims with gastroenteritis. Antimicrobial resistance tests revealed multiple resistance patterns and no strains were found to be resistant to ciprofloxacin or to the other quinolones tested. The poultry strains were found to be resistant to nalidixic acid, while the resistance in human strains was 31.8%. A combined analysis of resistance patterns and pulsotypes revealed four resistance patterns; the pattern associated with the outbreak was not correlated with the others present in the same period. This work suggests that a study of the relationship between different strains of the same serovar requires the implementation of different analytical methods.