No abstract

The proportion of salmonella carriers among town-nesting herring gulls increased significantly from 2.1% in 1975-6 to 8.4% in 1979. The range of serotypes carried by herring gulls was similar to that causing infection in man, and it is likely that the gulls ingest these serotypes when feeding at untreated sewage outfalls on the coast. This is supported by the proportion of salmonella carriers being higher among first-year birds (9.7%) than among older birds (2.0%), as it is known that higher proportions of immature herring gulls feed on the coast. Herring gulls carrying salmonellas appeared healthy at the time of capture and at a later date it was assumed that they were not themselves infected. However, their habit of congregating in large numbers on reservoirs and rubbish tips and also at resting sites on farmland often far from feeding and roosting areas, multiplies the pollution problem and increases the potential health hazard for both man and farm stock. Herring gulls feed at a variety of sites and fly many miles from food source to food source and from feeding areas to the roost. Thus, even within the same day, there is the possibility of the transfer of salmonellas over a much wider area than previously considered.

In 1988 there were two outbreaks of infection with Salmonella enteritidis phage type 4 in adjacent local authorities. The first affected 18 of 75 helpers and guests who attended a private function. Investigations revealed that home-made vanilla ice-cream containing uncooked eggs was the vehicle of infection and the causative organism was identified at the premises of the egg producer. The second affected 84 of 422 delegates attending a conference dinner, and 12 of 50 hotel staff at risk. A dessert made with lightly-cooked egg yolk and raw egg white was associated with infection, and the epidemic strain was cultured from the shell of an egg and an environmental sample from the producer's farm. It is of interest that one outbreak involved free-range and one battery-produced eggs, and that in one the vehicle was prepared at home and in the other in commercial premises. In neither incident was any deficiency in standards of egg production or catering practice discovered.

Twelve laboratories from 7 countries compared the productivity of refrigerated (72 h at 5 to 10°C) preenrichment and enrichment broth cultures with a standard cultural procedure for detection of Salmonella in 466 naturally contaminated low and high moisture foods. Refrigerated preenrichment and enrichment cultures identified 92.5 and 94.2% of contaminated samples, respectively. Variations in the ability of laboratories to successfully recover salmonellae under refrigeration test conditions were notable. Three laboratories found complete agreement between results by the standard and refrigeration test procedures and 5 additional laboratories reported >90% accuracy; lowest recovery rate for combined refrigeration results was 77%. Sensitivity of the refrigeration techniques was markedly greater with low than high moisture foods where the latter contributed all but two of the 62 false-negative results encountered in this study. Ability of individual laboratories to recover Salmonella from refrigerated preenrichment and enrichment broth cultures was not significantly different for given food categories. Productivity of paired enrichment-plating media differed widely with food type. Selective enrichment in tetrathionate brilliant green and plating on bismuth sulfite agar showed greatest sensitivity for isolation of Salmonella in high but not in low moisture foods where productivity of the 4 enrichment-plating conditions used in this study was comparable. Results on recoverability of Salmonella from refrigerated broth cultures concur with findings of an earlier comparative study and strongly support incorporation of this novel approach in standard cultural methods for detection of Salmonella in foods.