Unfortunately, there are no telltale signs that indicate if an egg is infected. But you can take precautions to reduce your risk of exposure.

Eggs can be contaminated with Salmonella if the hen that laid the egg is infected, but how common is this?

The type of bacteria that can get inside eggs, called Salmonella serotype Enteritidis (SE), comes from chickens whose ovaries are infected. The SE is passed along right into the egg.

According to the Centers for Disease Control and Prevention, only a small number of hens might be infected with SE at any point in time. Even if a hen is infected, it might still lay a lot of noninfected eggs, only sometimes passing along the bacteria.

Still, it's been estimated since the 1990s that about 1 in 20,000 eggs is contaminated with SE. That doesn't sound like many, but with about 65 billion eggs produced every year and just 30 percent diverted for pasteurization, that would mean about 2.2 million eggs a year could be contaminated with SE.

Although the CDC doesn't offer updated estimates, it does say that the proportion of Salmonella infections caused by this particular type of Salmonella declined by nearly one-third between 1996 and 2006. That's likely due to steps taken by both government and industry to reduce the incidence.

Take precautions
Unfortunately, there are no telltale signs that indicate if an egg is infected. But you can take precautions to reduce your risk of exposure.

First, like any type of bacteria, SE is killed when food is thoroughly cooked. That means it's safest to cook eggs until they no longer have a runny egg white or yolk.

In addition, keep eggs refrigerated until you're ready to cook them. Allowing them to stay at room temperature permits bacteria to multiply rapidly.

And, any egg-containing dishes -- including hard-boiled eggs -- should be consumed promptly. If they stay at room temperature (or anywhere between 40 and 140 degrees Fahrenheit) for more than two hours, throw them away.

It's especially important for people most at risk for foodborne illness to follow these guidelines. They include infants and young children, pregnant women, older adults, and people with weakened immune systems due to cancer treatment, diabetes, AIDS, and bone marrow or organ transplants.

SE can also infect broiler chickens -- chickens grown for meat, not to lay eggs. Keep safe by cooking chicken to at least 165 degrees (use a meat thermometer), and immediately and thoroughly washing your hands and any surfaces that come into contact with raw chicken.

Chow Line is a service of Ohio State University Extension and the Ohio Agricultural Research and Development Center.

For more safety tips, see Ohio State University's Food Safety website