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Salmonella and Eggs

SALMONELLA INFECTIONS IN EGGS FOR HUMAN CONSUMPTION

Salmonellae are common environmental contaminants. Infected wild animals and birds, and also humans, can be a source of infection for many species of farmed animals including poultry.Infection can be transmitted both by direct contact and indirect contamination (via boots, feed raw materials, clothing, hands, water etc.). The first outbreak of PT 4 S.enteritidis in a food animal in the United States (in layer chickens) was recently traced to a contaminated sewage outfall. This is a clear example of the infection in the human population occurred before that in the animal population. Both animals farmed intensively, and those farmed less intensively (barn, free-range etc.) are at risk.

On the basis of routine monitoring, primary breeding stock in the UK can usually be expected to be free of Salmonellae of special risk to human health (and of those of special risk to poultry health).The challenge for commercial farmers is to maintain this high health status for the life of the stock. However, infection of the animal does not equate to infection of the meat or eggs. Good quality eggs have strong natural defences for the control of Salmonella invasion. The effectiveness of this control mechanism is likely to depend on the original level and degree of tissue invasion of the infection, external and internal egg quality, basic hygiene during egg collection, handling and storage, and the temperatures at which eggs are stored.

Risk to human health will depend on the species of Salmonella involved, age and immune status of the person, and the number of bacteria ingested. Most surveys tend to examine the prevalence of infection rather that the number of bacteria present in those eggs which are positive. Because of the physical nature of the egg, cross-contamination between eggs and other foods in the kitchen is unlikely. However good hygiene in handling all perishable food materials is advisable.

The British Veterinary Poultry Association believes that the technology to reduce the hazard of Salmonella infections in eggs for human consumption is now well established. We would recommend the following:

• 1. Producers should take measures to identify infected and non-infected flocks.

• 2. Producers should also consult a poultry veterinarian when formulating a control strategy designed to prevent spread of infection.

• 3. Consider a multi-level approach to protection including

	Good site hygiene and isolation

	Control of insects and rodents

	Competitive exclusion

	Vaccination

	Good hygiene in egg collection, packing and storage

• 4. If cool-chain storage of eggs is to be used as means of reducing all bacterial replication within the eggs (along the lines suggested by the EU standing veterinary committee) this must include the retail chain. In any case refrigerated storage should, of course, be practised in the domestic kitchen.

• 5. Members of the human population at special risk (the very young and old, those suffering an immuno-suppressive disease and on immuno-suppressive medication) should take due care in the preparation of all food items to reduce or eliminate exposure to a wide range of pathogenic bacteria by following the cooking guidelines recommended by the PHLS. Such people may also need to take care to avoid environmental exposure to similar infections.