Inside the Egg
Until 1985, researchers thought bacteria lurking on the shell surface was the most likely source of salmonella contamination in eggs. Today, this risk is minimized because eggshells are washed and sterilized during processing. But researchers were surprised in the mid-'80s by a new finding -- salmonella lurking in the yolk membrane itself. These bacteria are literally born in the egg, entering from the infected ovaries of the laying hen, says Bessie Berry, manager of the United States Department of Agriculture's (USDA) Meat and Poultry Hotline. An added problem for the farmer is that the laying hen does not appear sick in any way.
The birds can become infected with salmonella in two ways: Either they're born from an infected mother hen, or they pick up salmonella along the way, perhaps when an unlucky fly lands on the hen's food tray and is gobbled up. Farm eggs and free-range eggs are not immune from contamination either, says Berry.
Testing the laying hens is the only way to determine infection. But testing is a staggering task when you take into account the numbers: There is one laying hen for every man, woman, and child in the United States -- about 260 million birds, according to FDA statistics. Finding the one infected egg in 20,000 is like looking for a needle in a haystack. Nevertheless, the FDA will require testing of commercial flocks -- the ones who lay the eggs for market -- by 2001.
"People think it won't happen to them, but it can," Berry says. Better to assume bacterial organisms are there and act accordingly.
Steps to Protect
Even if salmonella bacteria are within the egg, they still have to gain access to the nutrient-rich yolk to multiply -- a process hindered when the egg is fresh and the yolk membrane is intact. At that stage, the number of bacteria is very small. Refrigeration provides additional protection by limiting bacterial growth and preventing the breakdown of the membrane. So your best bet is to buy fresh eggs -- check the sell-by date on the carton, if there is one -- and keep them in the fridge. Also, make sure to use them within four weeks of purchase.