Listeria-tainted cantaloupe from Colorado is now being blamed for 8 deaths and 55 illnesses across 14 states, according to the Center for Disease Control (CDC) which expects numbers to continue to rise.

The outbreak is concentrated in Colorado, Texas, and New Mexico and Oklahoma, although cases of infection have been confirmed from California to Maryland.  (Click here to see a map of states with confirmed infections.)

Public health officials traced the source of contamination to Rocky Ford cantaloupes from Jensen Farm in Granada, CO, where testing of the fruit and equipment at their packaging facility confirmed a match of the strain Listeria monocytogenes.

Contamination of cantaloupes by Listeria is unusual, Salmonella being the pathogen more commonly found on the fruit.  The FDA is still investigating the source of the bacteria.

Unlike other melons, the rough rind on cantaloupes provides an ideal place for bacteria to flourish.

“It’s a great place for bacteria to hide out and persist,” said Trevor Suslow, a produce safety expert at the University of California at Davis. “It’s very hard to clean (even) with washing and scrubbing.”

Slicing into the fruit can transmit the bacteria into the flesh which is then eaten.

Furthermore:

“A lot of fruits are high in acid,” said Mike Doyle, director of the Center for Food Safety at the University of Georgia. “[Cantaloupe] aren’t.”

Their pH is close to neutral, providing the perfect environment for fostering bacterial growth. If the fruit are not refrigerated, bacteria flourish even more.

“They grow by gangbusters at room temperature,” Doyle said.

The voluntary recall is for cantaloupes shipped from Jensen Farm July 29 through September 10, 2011, which were distributed to at least 17 states.  The CDC predicts the number of people infected to rise, as the melons may still be in grocery stores and consumers’ homes.  Also, it can take up to two months to develop listeriosis after eating contaminated food.

Those most at risk are older adults, persons with weakened immune systems, pregnant women, and newborns. Symptoms usually include fever and muscle aches, diarrhea or other gastrointestinal symptoms, and the infection is treated with antibiotics.

The CDC urges immediate disposal of any Rocky Ford cantaloupes from Jensen Farms.