Food safety experts think the current listeria outbreak linked to cantaloupes is an "extraordinary" event because the bacteria that causes the disease is usually seen in deli meats and soft cheeses and not in produce.

Agents at the Food and Drug Administration are investigating how the contamination happened in produce (fresh vegetables or fruits in the same state as where they were harvested). But they have been prompt to ease consumer concerns.

"It's only when a strange alliance of the stars occurs you get an extraordinary event like this", said Jim Gorny, produce safety expert at the Food and Drug Administration, reports the Associated Press.  "It's a surprise that we'd have an outbreak of this extent so we really want to understand what happened."

Although it's rare, federal investigators have registered more listeria diseases linked to produce in the last two years. In 2009, they found listeria in sprouts. In 2010, on celery and now in cantaloupe, AP reported.

Colorado-based Jensen Farms, recalled Thursday 300,000 cantaloupes potentially contaminated with the devastating Listeria bacteria which is deadly to ethe lderly and people with weak immune systems.

So far, 22 confirmed cases have been reported in 7 states, with two deaths in Colorado and New Mexico, mostly in elderly patients.

Experts believe that listeria from a farm or packaging facility hit the outside of the fruit and then contaminated the inside when it was cut, said Dr. Robert Tauxe of the Centers for Disease Control and Prevention, according to the Associated Press.

Dr. Tauxe thinks victims may have kept the fruit in their refrigerator for some time, allowing the bacteria to grow, reports AP.

The CDC recommends the following to prevent listeriosis:

-Cook raw beef, pork or poultry thoroughly and store raw meat away from vegetables or cooked foods.-Rinse raw vegetables before eating.-Don't drink raw milk or products with raw milk-Wash hands and utensils after preparing uncooked foods

For more information on how to prevent Listeria visit the CDC website.