The death toll linked to listeria-contaminated cantaloupes in the United States has climbed to 28, the Centers for Disease Control and Prevention said on Tuesday.

Whole or pre-cut Rocky Ford-brand cantaloupe from Colorado-based Jensen Farms have been traced as the cause of what has become the deadliest U.S. food-borne listeria outbreak in a quarter century.

A total of 133 people in 26 states have fallen ill so far in the outbreak, and the CDC has said that one woman, who was pregnant at the time she fell ill, had a miscarriage.

The deadliest known food-borne listeria outbreak in the United States was in 1985 when a Jalisco Products' Mexican-style soft cheese contaminated with listeria killed 18 adults and 10 newborns, and caused 20 miscarriages.

The illness has a long incubation period, with symptoms sometimes not showing up until two months after people consume listeria-tainted foods.

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In a warning letter to Jensen Farms on October 18, the U.S. Food and Drug Administration said testing turned up widespread listeria contamination at its Granada, Colorado, packing plant, which "indicates poor sanitary practices in the facility".

The elderly, pregnant women and people with weakened immune systems are most at risk of falling ill from listeriosis. Symptoms include fever and muscle aches, sometimes preceded by diarrhea and other gastric problems.