What to Do About Listeria

It's pretty amazing, once you think about it, that you can walk into practically any grocery store in the U.S., pick up some meat, fresh vegetables and milk, take it all home and not have to be worried about whether it's safe to eat. After all, the basic sanitary principles for food processing were pretty well worked out decades ago. Every now and then, however, an outbreak of food poisoning comes along to remind us that nothing is perfect.

Take, for example, the report out of the U.S. Centers for Disease Control last week that at least a dozen people in the Northeast died this summer--and dozens more got sick--after becoming infected with listeria, one of the lesser-known bacterial causes of food poisoning.

This is the sort of news that could trigger a panic--especially because, for technical reasons, it can be very difficult to trace the source of a listeriosis outbreak. But with a little information about who is most at risk and how to lower what are already fairly slim chances of infection, you should have no trouble putting the latest developments in perspective.

Scientists have known for years that a group of tiny bacteria called listeria can cause illness in animals. But it wasn't until the early 1980s that scientists confirmed that humans can develop listeriosis as well. (A 1981 outbreak in Canada was tied to coleslaw prepared with contaminated cabbage.) As a rule, listeria is nothing healthy adults need to be worried about. "By the time they think that maybe they should go to the doctor, they start feeling better," says Linda Harris, a professor of microbiology at the University of California at Davis.

But a listeria infection can be quite serious for anybody with a weakened immune system. That includes the very old, the very young, cancer patients and those who are hiv positive. For these groups, mortality rates of 20% to 30% are common. About one-third of listeriosis cases occur among pregnant women; they usually survive, but they risk losing their unborn child. All told, about 500 listeria-related deaths are recorded in the U.S. each year. Fortunately, the number of cases seems to be on the decline.

Unfortunately, it's not always easy to distinguish listeriosis from other, more common food-borne illnesses. What you might think is food poisoning is often a viral infection. Typically, food poisoning is caused by one of several possible bacteria, including E. coli, salmonella, staphylococcus and listeria. Most of the time you can protect yourself against these pathogens by following a few simple safety rules. Washing your hands before and after preparing foods, for example. Or making sure all meat is thoroughly cooked. Or not using the same knife to cut uncooked poultry and chop fresh vegetables.

What's tricky about listeria is that unlike most food-borne pathogens, it can multiply in the refrigerator. Pasteurization and cooking will kill the listeria bacterium, but contamination often occurs later in processing. So you might bring home some ready-to-eat deli meats, hot dogs or soft cheeses that have a trace of listeria contamination on them, put them in the fridge and a week or so later, while they still look fresh, find yourself eating a listeria-packed meal. Not that you would know right away. The symptoms of listeriosis can take anywhere from a few days to a few weeks to show up.