(Kathryn Scott Osler  /  The Denver Post
Lead Food Lab Scientist Skip Gossack holds up a petri dish with the visible Listeria colonies from the Holly cantaloupe. Courtesy of denverpost.com.
Image: JoNel Aleccia
By JoNel Aleccia Health writer
updated 9/28/2011 3:20:32 PM ET 2011-09-28T19:20:32

Cantaloupe contaminated with listeria is nearing the end of its shelf life, but federal health officials warned Wednesday that more fatalities and illnesses can be expected through next month in the nation's deadliest food poisoning outbreak in more than a decade.

That's because the listeria bacteria that cause the infection have a very long incubation period compared to other foodborne pathogens, said Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention.

"It can be one to three weeks or two months in some cases," said Frieden, who urged people to toss any fruit from a Colorado grower responsible for the outbreak.

"For the public, it's important to know that if you know that the cantaloupe you have is not Jensen Farms, it's OK. If you're in doubt, throw it out," he added.

At least 72 people have been infected and 13 have died in 18 states in the widening outbreak traced to cantaloupes grown and shipped by Jensen Farms of Holly, Colo., CDC officials reported. At least three additional deaths are being investigated in Kansas, Wyoming and New Mexico, state health officials said.

The deaths top the nine killed in an outbreak of salmonella-tainted peanut butter nearly three years ago. In 1998, an outbreak of listeria in hot dogs and deli meat killed 21 people, according to CDC records.

Jensen Farms recalled its entire 2011 harvest of cantaloupe, more than 300,000 cases, on Sept. 14, because of potential listeria contamination, said Amy Philpott, a company spokeswoman.

Source of bacteria still unknown
The Food and Drug Administration still has not determined the source of the contamination, the first-ever listeria detected in cantaloupe, Commissioner Dr. Margaret Hamburg said. Traces of bacteria have been confirmed in cantaloupe from Jensen Farms and on equipment used to process it, the FDA said.

"The outbreak has been a tough one for all involved," she told reporters at a briefing Wednesday, adding later: "We at FDA are continuing to work on the root cause analysis."

The cantaloupe outbreak has led to deaths in eight states. Most of the victims of illness and death have been older than age 60, the CDC said, and many have health conditions that make them susceptible to the the bacteria's high mortality rate, which can top 20 percent.

Listeria is a common bacterium that typically causes mild illness in healthy people, but can cause severe illness in older people and those with compromised immune systems. It also can cause miscarriages and stillbirths in pregnant women and severe infections in new babies. In the current outbreak, two of the victims are pregnant, but the women and their babies appear to be doing fine, health officials said.

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Symptoms can include fever, diarrhea, nausea and muscle aches, sometimes severe.

While it's not clear yet clear exactly how the cantaloupes became contaminated, the fruit is susceptible because of its rough, porous skin and soft, succulent interior. In addition, knives can carry bacteria from the outside of the melon into the flesh when they slice through.

The contaminated cantaloupes were shipped between July 29 and Sept. 10 to 25 states, where they were sold at stores including large retailers such as Safeway, King Sooper and Walmart.

But companies said they responded quickly and none of the tainted melons should remain on store shelves, health officials said. Diana Gee, a spokeswoman for Walmart, said that firm pulled suspect cantaloupe from stores in 14 states at the first hint of problem, on Sept. 12, two days before Jensen Farms issued its voluntary recall.

The Rocky Ford-brand cantaloupes from Jensen Farms were shipped to Arkansas, Arizona, California, Colorado, Idaho, Illinois, Kansas, Minnesota, Missouri, Montana, Nebraska, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Virginia and Wyoming.

Some consumers may still have the contaminated fruit in their homes, possibly under refrigeration. Unlike many other foodborne pathogens, listeria bacteria can continue to thrive in cold temperatures.

Health officials urged consumers to check the labels on cantaloupes or to ask their grocers directly about the source of the fruit. Any contaminated cantaloupe should be tossed, and household surfaces should be sanitized with bleach, FDA officials said.

"We don't want you to trying to wash off that contamination," said Dr. Sherri McGarry, senior advisor of the FDA's department of Foods. "We want you to throw that produce away."

In any case, whole cantaloupe has a shelf life of about two weeks before it goes bad, while cut cantaloupe has an even shorter edible span.

This is the 10th outbreak of food poisoning in a decade tied to cantaloupe, Frieden said. Seven of those have been tied to salmonella contamination, while three have been in fruit tainted by norovirus.

CDC estimates that about 48 million people in the U.S. each year get sick from tainted food, with about 128,000 hospitalized and 3,000 deaths.

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