Ecological survey of Listeria in the Ferrara area (northern Italy).

A bacteriological survey was done on human and environmental specimens from the province of Ferrara in Northern Italy to determine the prevalence of Listeria spp. because no cases of listeriosis so far had been reported. Ten strains of Listeria spp. (1.9%) (7 L. monocytogenes, 3 L. innocua) were detected in 513 faecal specimens from asymptomatic humans, whereas none was recovered from 505 vaginal swabs of fertile women with discharges. Thirteen strains (9 L. monocytogenes, 4 L. innocua) were detected in 113 meat samples from retail outlets (11.5%), 4 strains (2 L. monocytogenes, 2 L. innocua) from 75 samples of frozen food (5.3%). Eleven Listeria strains (1 L. monocytogenes, 2 L. seeligeri, 1 L. welshimeri, 7 L. innocua) were isolated from 50 water samples of the river Po (22.0%); 15 strains (4 L. monocytogenes, 11 L. innocua) from 80 samples of other surface waters (18.8%); 1 strain (L. innocua) from 98 samples of groundwaters (1.0%); 14 strains (8 L. monocytogenes, 5 L. innocua, 1 L. seeliger) from 33 samples of urban sewage (42.4%). Only 35 (51.5%) of the Listeria isolates could be phage-typed. Analogies were observed between the distribution of Listeria and that of Salmonella, Yersinia and thermophilic Campylobacter in some materials in which these organisms were sought simultaneously.