More than one million eggs have been recalled since late January for possible contamination with listeria. Deli foods like cold cuts and hard-boiled eggs are often kept for weeks before they are used in the refrigerator, where listeria can grow like wildfire.

What did a Cobb salad and a chicken salad have in common that have made them the latest entries in a big ongoing food safety recall?

The answer is eggs. Hard-boiled eggs, to be precise. More than one million eggs bound for supermarkets, delis, and convenience stores have been recalled since late January for possible contamination with listeria monocytogenes, a bacterium that causes fever, nausea, and diarrhea, and can be deadly in the children and the elderly. No illnesses have been reported.

But the fact that the suspect eggs have made their way into products in in 34 states — from packaged egg salad sandwiches in Walgreens in California to garden salads at Wegmans stores in New York state — says a lot about the twisting paths that prepared foods can take on the way to the plate.

The recalled whole peeled eggs were sold packed in brine in 10- and 25-pound buckets by Michael Foods in Minnetonka, Minn.

Diane Sparish, a spokesperson for the company, tells The Salt her customers were food distributors, food service operators, delis, and food manufacturers. They liked the convenience of not having to cook the eggs themselves, she says. "Typically those products would be used as hard-cooked eggs in and of themselves, or in a finished product such as a salad."

The eggs were packed at the firm's facility in Wakefield, Neb., and shipped under six brand names, including Columbia Valley Farms and Wholesome Farms. The shelf life on the eggs is 45 days as long as the bucket hasn't been opened, according to the firm's website.

That seems like an awfully long wait to get to the plate, or the egg-salad sandwich.

Food-safety experts say that selling pre-cooked eggs in brine isn't in itself a risky undertaking. But all processed refrigerated foods are at risk of contamination. Listeria is a particular worry.

"Listeria grows extremely well in these types of foods," says Michael Doyle, director of the Center for Food Safety at the University of Georgia. The problem is amplified because deli foods like cold cuts and the hard-boiled eggs involved in this recall are often in the refrigerator for weeks before they are used, and listeria grows like wildfire at refrigerator temperatures.

"You will see grow from a few cells to millions or billions within a few weeks," Doyle told The Salt. He's done research to test that in deli meats like chicken and turkey, and says the growth of the pathogens was "incredible."

In recent years deli meat processors have taken steps to reduce the risk of contamination, including heat-processing packaged meats, and adding two chemicals, potassium lactate and and sodium diacetate, that together curb the growth of the bug.

Michael Foods identified a repair project in the packaging room as the likely source of contamination, according to Sparish. "Since then we've taken corrective steps to address the issue."

Doyle says that "in general I think deli products are safe." But he says eaters should be aware that just because something is fresh, it doesn't mean it hasn't had a lengthy wait in the wings. [Copyright 2012 National Public Radio]