An environmental survey of bakehouses and abattoirs for salmonellae

Abstract

1. Moore's gauze swabs have, in our hands, been shown to be a reliable instrument for the survey of salmonella infection in the environment of two food premises.2. A large bakery was demonstrated to be regularly contaminated with salmonellae. Thirty-one floor gully swabs out of 111 (27·9%) were positive for salmonellae. Little spread of infection to the general public was experienced.3. Staff infection with salmonellae was shown to occur in this bakery. Fifteen positive specimens of staff sewage out of 93 were obtained (16·1%). There was little evidence of prolonged contamination of the sewers with salmonellae. Staff infections were probably, therefore, of short duration. The staff probably became infected from contaminated goods in the bakehouse. Rat contamination of sewers was excluded by water trapping.4. It is not thought that regular examination of staff excreta would be a profitable means of discovering carriers or of preventing contamination of the products. The frequency with which such examinations would have to be performed to discover short-term excreters would be administratively impossible.5. Of 274 swabs from gullies in abattoirs, 111 were positive for salmonellac (40·5%). Twenty-one different serotypes were isolated. Seventeen of these serotypes are known to occur in animal feedingstuffs.6. Parallel examination of abattoir swabs and excreta from human infections for S. typhimurium, coupled with phage-typing of the strains, provided information of the geographically local nature of much sporadic illness due to this serotype. Of a total of 30 typable strains, 23 belonged to phage-types found in the abattoirs, or on local farms. Sporadic incidents were represented by 25 of these cultures, 18 of which corresponded in phage-type to those found in the abattoirs or in local farm animals. The phage-types of S. typhimurium isolated from the slaughter houses not infrequently corresponded in timing with the strains isolated from human infections.

Sewer and drain swabbing as a means of investigating salmonellosis

“…The bakery survey led to a similar study of Glamorgan abattoirs in 1957-9. In this investigation, phagetyping of strains of S. typhimurium enabled a detailed comparison to be made between abattoir and human isolations. The timing of recovery of the same phage-types from abattoir and man strongly suggested a causal association (Harvey & Phillips, 1961). Gauze swabs also proved of value in demonstrating the presence of S. typhimurium, type 12, in the environment of 15 out of 54 shops during an outbreak of salmonella food poisoning in Cardiff in 1960.…”

“…This incident led us to initiate a swab survey of bakehouses in . The investigation demonstrated the entry of salmonellas in raw ingredients of confectionery manufacture and the existence of minor or latent infections in members of bakery staff (Harvey, 1957;Harvey & Phillips, 1961). The bakery survey led to a similar study of Glamorgan abattoirs in 1957-9. In this investigation, phagetyping of strains of S. typhimurium enabled a detailed comparison to be made between abattoir and human isolations.…”

An outbreak of food poisoning caused by Salmonella typhi-murium, phage-type 12, probably spread by infected meat

“…Some samples of human sewage from Cardiff abattoir were also examined. The results are given in (Harvey & Phillips, 1961). From the records of the Veterinary Investigation Department, Cardiff, it was found that type 12 had been isolated from animals on three farms in SouthWales in 1959-60.…”

“…In a previous group of related cases due to S. typhi-murium, 1 a var. 3 (Harvey & Phillips, 1961), it had been possible to isolate the organism from farm animals in South Wales, from abattoir samples and from local human infections. In the present outbreak, we wished to follow the path of infection to retail food premises.…”

“…On inquiry, no common food and no single food premises are found to be implicated (Harvey & Phillips, 1961). Before the development of phage-typing of Salmonella typhi-murium (Felix & Callow, 1943;Callow, 1959;Anderson, 1960), many of the infections comprising such a group of related cases would have been regarded as sporadic.…”