"The problem is that listeria bacteria grows on produce -- in this case cantaloupes -- and occurs especially when proper precautions aren't taken at the farm or processing facility," Siegel said.
One possible contributor to the outbreak is inadequate facility and equipment design, which hampered thorough cleaning of surfaces the melons could touch, according to the report. Another possible route to contamination is a truck kept next to the processing line that went to and from a cattle operation.
In addition, the Colorado farm did not cool its cantaloupes before placing them in cold storage, which may have caused condensation that promoted the growth of listeria.
"This outbreak confirms the viability of raw produce, including cantaloupe, as a vehicle for listeriosis and highlights the importance of preventing produce contamination within farm and processing environments," the report noted.
Listeria is associated with about 1,600 infections in the United States annually, Silk said. A partnership between the CDC and state health departments, known as the Listeria Initiative, enabled the agency quickly to identify the source of the 2011 outbreak, he said.
The CDC continues to monitor and follow up on all listeria cases, Silk said. In addition, the FDA has stepped up inspections of cantaloupe farms and has issued guidelines to cantaloupe growers.
The best way to avoid listeria is to follow common-sense food-safety procedures, Silk said.
To help prevent infection, the CDC recommends you do the following:
- Rinse fruits and vegetables thoroughly under running water before eating, cutting or cooking them.
- Scrub farm produce, such as melons and cucumbers, with a clean produce brush.
- Dry produce with a clean cloth or paper towel.
- Separate uncooked meats and poultry from vegetables, cooked foods and ready-to-eat foods.
- Wash hands, knives, countertops and cutting boards after handling and preparing uncooked foods.
- Because listeria can grow in foods in the refrigerator, keep the temperature of your refrigerator at 40 degrees or lower and the freezer at 0 degrees or lower.
- Clean up all spills in the refrigerator, especially juices from hot dogs, lunch meat, raw meat and raw poultry.
- Clean the inside walls and shelves of the refrigerator with hot water and liquid soap, and then rinse.
- Thoroughly cook beef, pork or poultry.