Caution over Salmonella Surveillance
Concerned over the persistence of egg-borne Salmonella infection in
consumers, UK and EU authorities intend to introduce regulations to prevent sale
of shell eggs from flocks shown to be infected with either Salmonella
Enteritidis (SE) or Salmonella Typhimurium
(ST). By Simon Shane
Concerned over the persistence of egg-borne Salmonella infection in consumers, UK and EU authorities intend to introduce regulations to prevent sale of shell eggs from flocks shown to be infected with either Salmonella Enteritidis (SE) or Salmonella Typhimurium (ST).
Managers of farms would have to sample the environment of flocks at quarterly intervals in addition to annual visits for surveillance by authorized inspectors.
US Egg Quality Assurance Programs
Producers in the USA have operated in accordance with Industry or State Egg Quality Assurance Programs for over 10 years. A reduction in egg-attributed SE infection in consumers occurred following the introduction of the programs during the early 1990's.
FDA increase testing requirements
Due to the plateau in the incidence rate of SE outbreaks at 30 per year, the Food and Drug Administration
will require more frequent tests in an attempt to identify flocks which are infected. To date there has been no requirement for testing for Salmonella
Typhimurium or other paratyphoid serotypes.
Use of PCR tests
The contention by the British Egg Industry Council that environmental contamination does not equate to egg-borne infection is valid. The introduction of PCR
tests which are specific for either SE or ST in egg pools should be used as a confirmatory procedure following demonstration of either of the target organisms in environmental samples. A second problem relates to the proposed implementation of regulations. Given the extent of infection, an initiation date of 2008 is regarded as unrealistic.
Use of post-harvest methods
Health authorities should rather concentrate on post-harvest methods to reduce infection. Egg-borne paratyphoid infection was effectively suppressed in the USA in the 1970s following the advent of commercial egg washing.
Grading and packing installations in the USA subject eggs to non-immersion sanitation by successive washing at a water temperature of 54ÂºC at a pH of 12 and with a chlorine concentration in excess of 125 ppm.
This is followed by rinsing at a temperature of 60ÂºC with subsequent drying of the shell using filtered hot air.
A significant measure to reduce the potential for infection in consumers is to maintain a cold chain not exceeding 6ÂºC from the time of packing to the point of sale.
Pasteurized egg products
Commercial and institutional kitchens should use pasteurized egg
products displacing shell eggs where possible.
A program of education of consumers to refrigerate eggs and to exercise hygienic practices in preparation and thorough cooking of eggs has proven to be effective as components of a comprehensive method to prevent egg-borne salmonellosis.
These measures in addition to ensuring freedom from vertical infection from breeding stock to commercial chicks, acceptable biosecurity and diligent suppression of rodents and vaccination are all complementary to post-harvest modalities.
Placing the burden of Salmonella prevention on farmers
It would be unwise, impractical, ineffective and expensive to place the burden for Salmonella prevention entirely at the farm level, especially for farmers engaged in free-range production where biosecurity is at best rudimentary.
If public health and regulatory officials sincerely wish to reduce the incidence rate of egg-borne salmonellosis they would be advised to adopt a comprehensive program in cooperation with breeders, egg producers, processors and the food distribution industry.
By: Simon Shane
British Egg Industry Council
Articles on Salmonella
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