ABC News senior health and medical editor Dr. Richard Besser said today that while the eggs could have been contaminated at the factory, they could also have gotten the bacteria from the chickens themselves. Investigators are examining whether rodents were pooping in the chicken feed, possibly spreading the salmonella to the eggs.
Besser recommended cooking eggs not included in the recall thoroughly, while authorities investigate the contamination, and eating them immediately aftwerward.
The strain in question, Salmonella enteritidis, is particularly pernicious because it can affect the inside of an egg. The ovaries of a hen can be contaminated by the bacteria, passing the contaminant along to the whites and yoke of an egg as well as outside the shell, Braden said.
"The birds themselves aren't sick. The farmer doesn't even know what's going on. And in the meantime, it's producing eggs that look clean and fine," Braden said.
The federal government says its investigation into the source of the outbreak is ongoing, and while eggs are a prime suspect in many cases, other foods could also be involved. Officials have also not yet determined how salmonella got into the Iowa farm.
Already, one lawsuit has been filed in connection with an outbreak at a Kenosha, Wis. restaurant. A customer says she contracted Salmonella enteritidis there, and she's filed suit against both Wright County Egg and the restaurant, Baker Street Restaurant and Pub in Kenosha.
"Exactly how the salmonella came into the restaurant and whether there were cross-contamination issues in the restaurant or failing to cook within the restaurant, all of that is going to have to be worked out," said Bill Marler, the woman's Seattle-based attorney.
In northern California, officials noticed that dozens of people became sick after eating a certain kind of custard pie. In the southern part of the state, 12 people became ill after attending a catered event.
"It was traced back to the eggs they had consumed," said Dr. Angelo Bellomo of the Los Angeles County Department of Public Health. "At the same time we were doing this, similar incidents were being discovered in other parts of the country."
The U.S. Food and Drug Administration is still investigating the Iowa farm to try to find the source of contamination, though.
"Wright County Egg is fully cooperating with FDA's investigation by undertaking this voluntary recall," the company said in a statement. "Our primary concern is keeping salmonella out of the food supply and away from consumers."
Symptoms of salmonella-related illness could begin as many as three days after eating the eggs, and include fever, cramps and diarrhea, according to Besser. Cooking eggs thoroughly greatly reduces the risk of salmonella poisoning.