Cantaloupes infected with listeria have sparked the deadliest US foodborne disease outbreak in over a decade and are likely to claim more victims in the weeks ahead, officials said Wednesday.
Thirteen people have died and 72 have fallen ill after eating cantaloupe from Jensen Farms, in the first-ever outbreak of the pathogen in whole melons, the Centers for Disease Control and Prevention said.
Four distinct strains of listeria monocytogenes -- a bacterium that causes listeriosis and is among the most virulent foodborne pathogens -- have been traced to the Colorado-based farm, which issued a recall in mid-September.
The cantaloupes were distributed to at least 17 US states and some were exported.
Health authorities said the countries involved had been notified but were unable to immediately answer an AFP query about where they had been shipped.
A person can fall ill from listeria up to two months after consuming a contaminated product, and since listeria can linger for weeks even in cold temperatures like a refrigerator.
CDC director Thomas Frieden warned that the outbreak was likely to expand further.
"Listeria is an unusual bacteria," he told reporters.
"We do anticipate that there will be a rising number of cases in the days and weeks to come," he added.
Those most at risk are the elderly, people with weak immune systems, pregnant women, newborns and fetuses.
Pregnant women are often advised to stay away from deli meats and hot dogs, the more common potential sources of listeria, which can cause miscarriage or still birth.
Two of the 72 people who have fallen ill are pregnant women, but they and their fetuses are "doing OK," Frieden said.
Listeria infections typically cause fever and muscle aches.
"This outbreak has been a tough one for all involved," said Margaret Hamburg, commissioner of the Food and Drug Administration.
"It is the first time we have seen listeria contamination in whole cantaloupe and we are working very hard to try and figure out how this happened," she said.
"We will see more cases, likely through October."
The FDA has warned consumers not to eat Rocky Ford Cantaloupe shipped by Jensen Farms and to throw away the recalled cantaloupes "in a sealed container so that children and animals, such as wildlife, cannot access them."
Not all the afflicted cantaloupes are labeled, but those that are would carry "a green and white sticker that reads: Product of USA - Frontera Produce-Colorado Fresh-Rocky Ford - Cantaloupe," the farm said.
Alternatively, it could have a "gray, yellow, and green sticker that reads: Jensen Farms-Sweet Rocky Fords."
The farm has not said how many cantaloupes were recalled. A statement on the farm's website said the owners "are deeply saddened" to learn of the outbreak and are "cooperating fully with public health officials."
Investigators are looking at the possibility that animal intrusion may have caused the outbreak, and they are also probing water quality and the growing and harvesting practices at the family-owned farm.
Local experts in Colorado and examiners from the FDA "are at the farm conducting an environmental assessment to get to the heart of what may have happened," said Sherri McGarry, senior advisor at the FDA's Office of Foods.
The last major deadly US outbreak of listeria was in 1985 when the bacteria was found Mexican-style cheese in southern California, causing 29 deaths, the CDC said.