EU Salmonella targets – legislating against the principles of epidemiology

The European Commission issued Directive IP/06/1082 on August 1st establishing targets for the reduction in prevalence rate of “Salmonella” in flocks producing table eggs. In addition regulations were finalized harmonizing control measures which rely on vaccination.

These are worthy aims if the intent is to reduce incidence rates of salmonellosis in consumers attributable to egg-borne infection with Salmonella enterica ser. Enteritidis (SE).

Unfortunately, simply promulgating a regulation does not necessarily have the desired effect, irrespective of how legislators in Brussels may feel as they leave for their extended weekends.

The incidence rate of SE in consumers in the USA has been reduced from a rate of 10/100,000 in the early 1990s to 2/100,000 in 2002. This has required a coordinated multi-level approach to suppression of which vaccination is only a single component. The National Poultry Improvement Plan established standard procedures for monitoring flocks and their environment and specified microbiological procedures to isolate and identify SE. Grandparent and parent flocks were then tested and certified to be free from the vertically transmitted infection. Producers agreed to conform to voluntary State and Industry sponsored Egg Quality Assurance Programs which mandate standards of biosecurity, rodent control and management practices which reduce the probability of infection. Surveillance procedures involving environmental sampling are required. The intensity and frequency of testing will be increased in 2007 in accordance with an FDA mandate as there are still approximately 30 confirmed SE outbreaks annually and possibly 120,000 incident cases in the US population. Eggs from flocks shown to be infected with SE are diverted to breaking and pasteurization (5 log reduction) or the flocks are depleted if near the end of their laying cycle. Vaccination is routinely employed using successive doses of mutant live Salmonella Typhimurium vaccine during rearing and where a history of SE exists on a farm, inactivated SE emulsions are administered.

Eggs are routinely sanitized by spray (non-immersion) washing and rinsing followed by drying before packing. The USDA-FSIS mandated rapid cooling, storage and transport of eggs at a temperature not to exceed 7C during the mid 1990s. Education campaigns were instituted to encourage consumers and institutional kitchens to apply hygienic procedures in food preparation and to cook eggs thoroughly. Most commercial establishments now use pasteurized products which represent 30% of egg output.

The resolution of a complex problem cannot be achieved by simplistic imposition of a regulation imposing vaccination as a single modality and establishing targets for reduction in prevalence. The positive advances in control of SE in the USA were stimulated by Industry leaders who were aware of the marketing implications of a “contaminated product image” and fear of liability claims in the active civil tort system. Industry has cooperated with State and Federal regulators to achieve progress in the suppression of infection.

By: Simon Shane