Twenty-five people have died so far as a result of a listeria outbreak linked to Colorado-grown cantaloupes -- the deadliest known case of foodborne illness in the U.S. in more than 25 years.

The Centers for Disease Control and Prevention said 123 people have been sickened across 26 states, including the deaths. Those who have died ranged in age between 48 and 96, with a median age of 87. 

There have been six deaths in Colorado; five in New Mexico; two each in Texas, Kansas, New York and Louisiana; and one each in Indiana, Maryland, Missouri, Nebraska, Oklahoma and Wyoming. In addition, a pregnant woman had a miscarriage after she fell ill. And more people could still die, according to the CDC, as the number of illnesses may continue to grow. 

Symptoms of listeria can take up to two months to appear, which include fever, muscle aches, stiff neck, confusion and diarrhea or other gastrointestinal problems.

The disease is most deadly among high-risk groups, such as the elderly. The current outbreak is worse than a 1998 spate of listeria infections, when 21 deaths were linked to tainted hot dogs and delicatessen meats.

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The contaminated melons, which were recalled in September, should be off store shelves by now. 

Four strains of listeria monocytogenes have been traced to Rocky Ford melons produced by Jensen Farms in Holly, Colo. 

Pools of water on the floor and old, hard-to-clean equipment at the farm's cantaloupe packing facility were probably to blame for the outbreak, according to the Food and Drug Administration. 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 a six-page assessment of the conditions at the farm based on investigators' visits in late 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, as pools of water potentially harboring the bacteria formed close to the packing equipment.

The equipment – purchased in July, the same month the outbreak started – was previously used for a different agricultural commodity, the agency said, and the listeria "could have been introduced as a result of past use of the equipment," according to the report.

The 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 farm did not use a process called "pre-cooling" that is designed to remove some condensation, which creates moist conditions on the cantaloupe rind that are ideal for listeria bacteria growth. Listeria grows in cool conditions, unlike most pathogens.

Another possible source of contamination was a truck that frequently hauled cantaloupe to a cattle operation and was parked near the packing house.

Contamination could have been tracked into the house by people or equipment, the report said.

Barbara Mahon of the CDC said that the illnesses peaked from mid-August through September, but that the government would continue to monitor the situation for at least another two weeks.

FDA officials said Wednesday that the agency has never visited the farm to do an inspection, but that would likely change under a new food safety law signed by President Obama earlier this year that boosts the number of inspections the FDA conducts annually. Currently, the agency may only visit a food facility every five or 10 years at the most.

FDA officials said they have visited many food facilities over the years and the conditions at Jensen Farms were unique.

"There is no reason to believe these practices are indicative of practices throughout the industry," said Sherri McGarry, a senior officer in FDA's office of foods.

McGarry said the agency has sent the company a warning letter and is still considering what enforcement actions it will take. Officials said the farm had cooperated in all aspects of the recall and investigation.

Messages left for the farm's owners were not immediately returned.

The Associated Press and NewsCore contributed to this article.