Epidemiology of Salmonella enterica serotype Enteritidis infections in southern Italy during the years 1980-1994

Increased frequency of identification of Salmonella enterica serotype Enteritidis as a causative agent of sporadic and epidemic cases of infection in humans, along with isolation in many parts of the world of strains belonging in a large proportion to a few phage types, has made phage typing alone inadequate for epidemiological investigations. In southern Italy the epidemic increase in isolation of S. enterica serotype Enteritidis that has been observed since 1990 has been associated in approximately 80% of isolates with phage type 4 (PT-4), in agreement with the epidemiological observations from other European countries. We have applied polymerase chain reaction (PCR) ribotyping in association with phage typing to a sample of non-outbreak strains and to all the outbreak strains sent for identification and typing to the Southern Italy Centre for Enterobacterial Pathogens between 1980 and 1994 from hospital and public health laboratories. This technique identified 15 distinct profiles among the 405 strains examined. Whereas a single profile (PCR ribotype a1) appeared to be closely related to PT-8, and to characterize a high percentage of the strains circulating during the early non-epidemic years (1880-1985), 11 patterns were recognizable within PT-4, and 5 within PT-1. Some of these apparently emerged after 1990. This subdivision enabled attribution of the epidemic circulation of PT-4 to multiple clones of S. enterica serotype Enteritidis.