WASHINGTON -- Pools of water on the floor and old, hard-to-clean equipment at a Colorado farm's cantaloupe-packing facility were probably to blame for the deadliest outbreak of foodborne illness in 25 years, the Food and Drug Administration said yesterday.
Government investigators found positive samples of listeria bacteria on equipment in the Jensen Farms packing facility and on fruit that had been held there.
In the assessment of the conditions at the farm based on investigators' visits in September, the FDA said Jensen Farms had recently purchased used equipment that was corroded, dirty and hard to clean. The packing facility floors were also constructed so they were hard to clean, so pools of water potentially harboring the bacteria formed close to the packing equipment.
The dirty equipment -- purchased in July, the same month the outbreak started -- was previously used to wash and dry potatoes, the agency said, and the listeria "could have been introduced as a result of past use of the equipment," according to the report.
FDA officials said that they are not concerned about similar listeria contamination in the potatoes that were previously processed on the equipment because those vegetables are rarely eaten raw. Cooking can kill the bacteria.
A warning letter from the agency to Jensen Farms said that a third of 39 swabs taken throughout the facility tested positive for listeria.
"This significant percentage of swabs that tested positive for outbreak strains of (listeria) demonstrates widespread contamination throughout your facility and indicates poor sanitary practices in the facility," the letter said.
Though the agency said the contamination likely happened in the packing house, the way the cantaloupes were cooled after being picked may have exacerbated the listeria growth. The farm did not use a process called "pre-cooling" that is designed to remove some condensation, thus creating moist conditions on the cantaloupe rind that are ideal for listeria bacteria growth. Listeria grows in cool environments, unlike most pathogens.
FDA said that samples of cantaloupes in Jensen Farms' fields were negative for listeria, but bacteria coming off the field may have initially introduced the pathogen into the open-air packing house, where it then spread. Listeria contamination often comes from animal feces or decaying vegetation.
The Centers for Disease Control and Prevention says 123 have been sickened in the outbreak, including the 25 who died.