(CNN) -- Unsanitary conditions at a Colorado cantaloupe farm's packing facility are a possible contributing cause of one of the nation's worst outbreaks of listeria contamination in food, the Food and Drug Administration said Wednesday.
Meanwhile, a Centers for Disease Control official said it is too early to declare the outbreak over, but the number of new cases appeared to be diminishing.
"The peak in illnesses appears to have occurred from late August until the middle of September," said Dr. Barbara Mahon of the CDC, who added that additional monitoring will be needed for at least another two weeks.
The FDA said it was unable to pinpoint the definitive cause of the outbreak, which has been linked to 25 deaths so far.
An FDA letter to Jensen Farms of Granada, Colorado, however, cited violations in sanitary conditions that must be addressed. It said tests showed "widespread contamination throughout your facility and indicates poor sanitary practices in the facility."
The likely causes included packing equipment that "was not easily cleaned and sanitized" and the use of washing and drying equipment for cantaloupe packing as well as other raw agricultural commodities.
In addition, the agency said in a statement, the facility lacked a "pre-cooling step" to remove field heat from the cantaloupes before cold storage, possibly leading to condensation in the cooling process that promoted growth of the listeria bacteria.
A letter dated Tuesday from the FDA to Jensen Farms cited violations in sanitary conditions. The letter said tests at the facility found listeria bacteria contamination.
"These positive swabs were taken from different locations throughout the washing and packing areas in your facility, all of which were either food contact surfaces or areas adjacent to food contact surfaces," the letter said. "This significant percentage of swabs that tested positive for outbreak strains of Listeria monocytogenes demonstrates widespread contamination throughout your facility and indicates poor sanitary practices in the facility."
According to the letter, the company has 15 days to document steps it has taken to correct the problems. The letter also said the company notified the FDA on Monday that it agreed to inspection by the agency of its growing, packaging, and cold storage operations before it resumes food harvesting, packaging, or processing.
Jensen Farms also agreed to correct all objectionable observations noted during said FDA inspections, the letter said.
A total of 123 people in 26 states have been infected by the listeria outbreak, the Centers for Disease Control and Prevention says. Additionally, a woman who was pregnant at the time of her illness had a miscarriage, the agency said.
The listeria outbreak is the deadliest food-borne illness outbreak in the United States since 1998.
Groups at high risk for listeria include older adults, people with weakened immune systems and pregnant women.
Jensen Farms issued a voluntary recall of its Rocky Ford brand cantaloupes on September 14. The tainted cantaloupes should be off store shelves, the CDC has said.
Cantaloupes from Jensen Farms should be disposed of immediately, even if some of them have been eaten, the agency recommended. If consumers are uncertain about the source of a cantaloupe, they are urged to ask their supermarket. If the source remains unknown, the fruit should be thrown out.
Refrigerating a cantaloupe will not kill the bacteria, which can grow at low temperatures, and consumers should not try to wash off the bacteria.