Sewer and drain swabbing as a means of investigating salmonellosis

The use of gauze swabs in drains or sewers to clarify the path followed by a salmonella from source to human host has been reviewed in the light of experience gained in Cardiff over 15 years. This period has seen a marked change in attitudes to salmonella epidemiology in that infected food is now regarded as of greater importance than infected food handlers. In these 15 years, butchers, abattoirs and knackers' yards, markets and bakehouses have been monitored. In the bakehouse survey the existence of staff infection was demonstrated by sewage examination. Sewage investigation has also been used to show frequent entry of salmonellas into households in a residential estate. The estate was carefully chosen to exclude salmonellas from industrial sources and shops. The frequent finding of infection in this sewage implies that a commonly consumed heavily infected food item is involved. The wide range of serotypes isolated suggests an animal usually fed on infected animal feed. Poultry and pigs are put forward as animals liable to spread salmonellosis to man.It is hoped that clarification of the salmonella pathway may eventually lead to measures likely to prevent the transmission of infection to man. It is also suggested that swabs placed in abattoir drains serve as an economical method of obtaining warning of a persistent build-up of contamination. The persistence of a serotype in an abattoir is not infrequently followed by human infection.