Epidemiological studies on Salmonella in a certain area ("Walcheren Project"). IV. The incidence of Salmonella in the sewage system, in the faeces of man and pets as well as in shops, kitchens and lavatories in the village of Aagtekerke.
As part of the epidemiological investigations on Salmonella ion the former island of Walcheren, the contamination of sewage water in the village of Aagtekerke was studied over a prolonged period of time. These studies showed that this sewage water was frequently contaminated by large numbers of Salmonella. In the present study efforts were made to find the source of this contamination and for this purpose the incidence of Salmonella in the sewage system, in the faeces of man and pets as well as in shops, kitchens and lavatories in the village of Aagtekerke was studied for a period of three weeks in June 1977. Salmonella was only isolated from a few samples of faecal material of human and animal origin, and from the sewage system (including the inlet water and effluents of the sewage works). Serotyping showed that the strains isolated from human faeces were similar to those found to be present in the sewage system. This fact taken in conjunction with the results of the bacterial counts, suggests that the sewage system was only contaminated by a small number of carriers. The reduction of contamination observed in the sewage system during the period of investigation could be evidence that Salmonella organisms cannot survive by themselves in an environment of this type, at least not at the temperatures recorded when collecting samples from the sewage water. Growth of organisms under more favourable conditions cannot be ruled out. A questionnaire about the dietary habits and kitchen hygiene of the local population showed that contamination within households, originating with the food, is a real possibility.