Salmonella in effluent from sewage treatment plants, wastepipe of butcher's shops and surface water in Walcheren.

In the frame of the "Walcheren-project" in which the epidemiology of salmonellosis is studied in a certain area, effluent from sewage treatment plants, wastepipe's of butcher's shops and surface waters, which receive the effluent were studied for the presence of salmonellae. From 160 samples of effluent 150 (94%) contained salmonellae. The most common serotype was S. typhi murium (35%) followed by S. panama and S. infantis. 14 butcher's shops' wastepipes were sampled 54 times. 14 (26%) times salmonellae were found, but only twice was the type isolated from the butcher's shop the same as found in the effluent on the same day. With regard to the presence of salmonellae in surface waters receiving effluent it was shown that from the immediate vicinity of the plant to 250 m downstream from the site of drainage of effluent the number of salmonellae per 100 ml remains almost constant. After 1.5-4 kilometers Salmonella could not be isolated from any of the samples examined. The results underline the hypothesis that salmonellae multiply in the sewage system and/or plant. The spread of samonellae by effluent seems to be limited to the plant itself and of the nearest vicinity. Proposals are brought forward to interupt contamination cycles by decontamination measures.