Occurrence of 'thermophilic' campylobacters in sewage and their removal by treatment processes.

Removal of thermophilic campylobacters from sewage at three different stages of treatment at a trickling filter sewage works has been assessed. Samples of incoming sewage, primary sedimentation effluent and final effluent were taken daily from 06.00 h to 20.00 h for 5 consecutive days and the numbers of campylobacters determined by using a most probable number method. Each sample was cultured using 2 h pre-enrichment followed by enrichment in Preston broth for 48 h and detection by plating. Over 78% of the incoming campylobacters were removed after primary sedimentation and less than 0.1% remained in the final effluent. Campylobacter jejuni biotype I and biotype II constituted 81.5% and 15.9% respectively of the 232 isolates tested. Serotypes common in sewage were common in human faeces. It appears that the trickling filter sewage works removes most of the campylobacters entering the sewage works, but large numbers, estimated to be approximately 10(10), are released into the environment daily from a local sewage works.