The CDC reports that at least 13 people have died and 72 have become ill from eating cantaloupe tainted with the bacterium Listeria monocytogenes. The source of the Listeria outbreak has been traced to Rocky Ford brand cantaloupes grown by Jensen Farms in Granada, Colorado.

Illnesses have been reported in 18 states from California to Maryland, with the largest number (15) in Colorado. A report issued by the CDC in late 2010 estimates that one in six Americans get sick every year from the food they eat.

Listeria infections primarily occur in older adults, pregnant women, newborns and adults with weakened immune systems. The CDC said the median age of those sickened is 78 and that one in five who contract the disease can die.

It can take four weeks or longer for a person to fall ill after eating contaminated food. So the number of cases in the current outbreak is almost certain to grow.

The CDC recommends that people at highest risk for infection and anyone else who wants to reduce their risk of Listeria infection not eat any cantaloupes marketed as coming from Jensen Farms. Cantaloupes known to have come from Jensen Farms should be disposed of in a closed plastic bag placed in a sealed trash can. This will prevent people or animals from eating them.

Surfaces touched by the suspect cantaloupes should also be cleaned and sanitized. Bacteria on the outside of the fruit or vegetable can be transmitted to the inside by the knife used to cut the produce. This means that it is important to wash the outside of produce, even in a case such as cantaloupes where the outside is not being eaten. Given the current Listeria outbreak, if you have a cantaloupe from Jensen Farms, or are unsure where your cantaloupe is from, however, just throw it away. Do not eat it.

Tainted cantaloupes were shipped from July 29 through September 10 to at least 25 states. On September 14, Jensen Farms began a voluntary recall of its cantaloupes.

Some recalled cantaloupes are labeled "Colorado Grown," "Distributed by Frontera Produce," "" or "Sweet Rocky Fords." But not all of the recalled cantaloupes are labeled with a sticker.

Though Salmonella outbreaks are better known and cause more illnesses, Listeria outbreaks cause more fatalities. Twenty-one people died in an outbreak of Listeria poisoning in 1998 traced to contaminated hot dogs and deli meat. A larger Listeria outbreak in 1985 killed 52 people and was linked to Mexican-style soft cheese.

About 800 known cases of Listeria occur yearly in the United States, according to CDC, and there usually are three or four outbreaks. Most of these are traced to deli meat and soft cheeses, Produce has rarely been the culprit, but federal investigators say they have seen more produce-related Listeria illnesses in the past two years. Listeria was found in sprouts in 2009 and celery in 2010.

While eating Listeria-tainted food often causes no ill effects in healthy adults, it can kill the elderly and those with compromised immune systems. It's also dangerous to pregnant women because it easily passes through to the fetus.

Symptoms of Listeria infection usually include fever and muscle aches, often preceded by gastrointestinal problems such as diarrhea. Listeria has a long incubation period. It can take four weeks or longer for a person to fall ill after eating contaminated food. So the number of cases in the current outbreak is almost certain to grow.

If this seems like one in an ever-growing series of outbreaks from contaminated food, that's because it is.

For more information on Listeria and Listeria infections, see the CDC's Listeria homepage. The CDC also regularly posts updates on the current Listeria outbreak.