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The largest egg recalls in U.S. history just happened to coincide with the implementation of the FDA’s Egg Safety rule in summer 2010. While many egg producers were already operating under state or voluntary Salmonella prevention programs prior to 2010, the nationwide implementation of FDA’s rule seems to have had a positive impact on Salmonella enteritidis (SE) incidence in layer houses and in eggs.
Iowa State University’s Veterinary Diagnostic Laboratory reports that the percentage of the layer house environmental samples that it tests that are positive for SE has dropped from 24.5 percent in 2010 to 2.5 percent in 2015, a reduction in the rate of positive samples of 90 percent. The laboratory tests about 13,000 environmental samples annually. Approximately 60 percent of the samples originate from Iowa egg farms, and the remainder from sites located in more than a dozen other states.
“The test data also show that the likelihood of a positive environmental test translating into contaminated eggs is extremely low,” said Hongwei Xin, director of the Egg Industry Center at Iowa State. “It’s a very positive outcome of the industry implementing the federal egg safety rules that went to effect in July 2010.”
Potential reasons given for the significant drop in positive samples may include an increase in flocks that are vaccinated for the Salmonella bacterium, according to Xin. It is now estimated that about two-thirds of the country’s layer flock is administered an SE vaccine, up significantly from 2010. There also has been heightened awareness and training in Salmonella enteritidis prevention, he added.
When an environmental sample tests positive, the FDA requires testing of shell eggs from that facility — four consecutive tests of 1,000 eggs each done at specified intervals. Once received by the Veterinary Diagnostic Laboratory, eggs are separated into egg pools; a pool consists of the contents and shells of 20 eggs. Scientists culture samples from the egg pools to detect the presence of the Salmonella bacterium.
Following these FDA protocols, the Veterinary Diagnostic Laboratory tested more than 35,000 egg pools from 2010 to 2015. In that time period, only one positive egg pool was identified, which occurred during the time frame of a 2010 national egg recall. No positive egg pool tests have been found to be positive for SE in the past four years.
Egg producers should be proud of the progress they have made in keeping SE out of the layer house. Many of the activities designed to keep Salmonella out, like rodent and fly control measures, have also served to enhance overall farm biosecurity.
It now seems that a cage-free U.S. egg industry is a distinct possibility, and this will provide an even greater challenge for producers to keep eggs SE free. Cage free means floor eggs and birds will have more contact with feces. Keeping rodents and other potential SE vectors out of the hen house will be more important than ever.