Salmonella is declining in Ireland

Researchers attributed this decline to the control strategies employed by the Island of Ireland.

July 12, 2007

In the 1980's there was a dramatic increase in the human outbreaks of Salmonella enteritidis (SE) phase type 4 in the United Kingdom and Western Europe. In recent years, there has been a decline in the incidence of SE in the United Kingdom. Much of this reduction has been attributed to the Lion Quality Code of Practice implemented in the United Kingdom in 1998. This program covers about 85 percent of the eggs produced. It requires that all flocks are vaccinated against SE. There are also controls on welfare, hygiene, and biosecurity. The Republic of Ireland does not permit vaccination for SE, but they do monitor feed and flocks for SE. Any flocks testing positive for SE must be slaughtered.

Considering the above trends, Murchie et al., 2007 (Journal of Food Protection 70:1238-1240) surveyed approximately 30,000 eggs from Ireland for the incidence of Salmonella. From 30,108 eggs, 5,018 samples were analyzed. Samples included 2,503 from Northern Ireland and 2,515 from the Republic of Ireland. These samples included 51 percent from intensive production, 24 percent from free-range, 14 percent from barn production and 11 percent from organic flocks. Flocks from the Republic of Ireland were not vaccinated while 87.6 percent of the Northern Ireland flocks were vaccinated.

Salmonella contamination was detected only on the shells of two samples with no contamination found in egg contents. Salmonella infantis and Salmonella Montevideo were identified. No SE was detected. The percent positive was reported to be 0.04 percent. Wilson et al., 1998, (Commun. Dis. Public Health 1:156-160) observed 0.43 percent Salmonella contamination in 1996 to 1997 samples from Northern Ireland. Another study in 2001 (Advisory Committee on Microbiological Safety of Food, Her Majesty's Stationery Office, London) reported 0.99 percent Salmonella contamination from 13,970 samples collected from England in 1995 to 1996. Murchie et al. concluded that these studies indicate a downward trend in Salmonella contamination during the last decade in the United Kingdom. They attributed this decline to the control strategies employed by the Island of Ireland.

How United States Compares

Gast, 2000 (Egg Nutrition and Biotechnology, edited by Sim, Nakai and Guenter, publisher CAB International) reported an overall incidence of internal contamination in shell eggs with SE to be 0.01 percent or lower in the United States. He concluded that most contaminated eggs contain small numbers of SE cells. The egg industry in the United States has implemented programs to control pests (rodents), cleaning and disinfection of facilities between flocks, and increased biosecurity measures.

Processing has also received greater emphasis including the requirement that all shell eggs marketed in the United States must be held at 7°C (45°F). Also, all shell eggs are washed and sanitized to minimize SE contamination on the shell surface. When considering further processed egg products, pasteurization is required to assure that all Salmonella contamination is eliminated.

It is encouraging that there appears to be a decline in the incidence of Salmonella contamination in shell eggs. This indicates that expanded control methods are showing benefits. There, of course, is a continuing need to further improve methods for controlling SE in eggs.