Salmonella in raw shell eggs in Northern Ireland: 1996-7.

The shells and contents of 2090 packs of six raw eggs from shops in Northern Ireland were examined for the presence of salmonella between April 1996 and October 1997. Nine isolates of salmonella were detected from separate packs of eggs (0.43%). One of the isolates was from egg contents (0.05%), where salmonella can proliferate to levels likely to cause human infection if the egg is inadequately cooked. Visible dirt and organic contamination were poor predictors of salmonella contamination since most contaminated eggs had apparently clean and uncracked shells. Contaminated eggs were more likely to have been sold from small shops than supermarkets. Sampling for uncommon pathogens is expensive, labour intensive, and yields many negative results. The small numbers of positive results make it particularly susceptible to variations between methods. It continues to be important to cook eggs thoroughly to eliminate the risk of salmonellosis since this survey suggests that over 10,000 boxes containing one or more contaminated eggs may be sold in Northern Ireland each year. Caterers should use pasteurised liquid egg. A system of branding to enable eggs to be traced to individual flocks would assist in the investigation of outbreaks.