Sewer and drain swabbing as a means of investigating salmonellosis

Abstract

SUMMARYThe 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.

Salmonella surveillance with reference to pigs – Cardiff abattoir, 1968–1975

“…(Harvey, 1957). It was natural to extend the technique to abattoirs and other premises (Harvey & Price, 1970 Total paired samples, 3430. Positive samples, 394 (11.5 %).…”

“…These foci were plotted on a large-scale map and an attempt was made to associate their geographical position with the occurrence of local paratyphoid B outbreaks. The swab monitoring technique was later extended to detecting salmonellas in bakeries, abattoirs, butcher's shops, markets and human sewage (Harvey & Price, 1970). The drain swab, therefore, became a natural sample to monitor salmonellas in Cardiff.…”

A Survey of Argentine and Lebanese Bone for Salmonellas with Particular Reference to the Isolation of Salmonella typhimurium

“…We have noted elsewhere that any single enrichment medium, if inoculated with material containing two salmonella serotypes, may have a bias towards permitting more rapid multiplication of one of them (Harvey & Price 1970). This problem is very relevant to the conduct of unbiased surveys and has been studied in a paper in which bias in favour of the isolation of certain serotypes was recorded for two commonly used enrichment media (Harvey & Price 1976).…”

“…COMPARISON OF SALMONELLA serotypes isolated from man and his environment is a recognized means of investigating salmonella epidemiology. The technique has been of value in associating bakery and abattoir sources and human infection (Harvey 1957;Harvey & Phillips 1961;Harvey & Price 1970). The association method has been applied to domestic animal salmonellosis with the conclusion that salmonellacontaminated animal feed has little relevance to the incidence of serotypes commonly infecting cattle-Salmonella typhimurium and S .…”

Salmonella isolation from hospital areas

“…Sewer swabs were first used in Cardiff, in 1955, to associate a butcher's shop with an outbreak of salmonellosis (Harvey & Price 1970). Since then, they have often been employed in the investigation of salmonella epidemiology.…”