Two more people in the United States have died from eating listeria-tainted cantaloupes, bringing the death toll to 15 in the country's deadliest foodborne outbreak in more than a decade, health officials said on Friday.

The outbreak has focused new attention on listeria as a possible contaminant of fresh produce. On Friday, California-based True Leaf Farms recalled almost 15,000 bags of chopped romaine lettuce that may be contaminated with listeria, although no illnesses have been reported and officials said the incident had no direct link to the deadly cantaloupe-related outbreak.

Listeria monocytogenes is a frequent cause of U.S. food recalls in processed meats and cheeses, but contamination in fresh produce is a new and worrisome development.

According to the U.S. Centers for Disease Control and Prevention, the multistate listeria outbreak caused by tainted cantaloupes shipped by Colorado-based Jensen Farms has killed 15 and infected 84 people in 19 U.S. states.

That is up from 13 deaths and 72 people infected in 18 states as of Wednesday.

Of the 15 deaths, five were in New Mexico, three were in Colorado, two were in Texas, and there was one each in Kansas, Maryland, Missouri, Nebraska and Oklahoma.

The CDC said on Wednesday it expected more infections and possibly deaths in the outbreak because listeria had a long incubation period, with symptoms sometimes not showing up until two months after people consume listeria-laced foods.

NEW FOCUS ON LEAFY GREENS

Food and Drug Administration spokesman Douglas Karas said on Friday there was no connection between the lettuce recall and the cantaloupe outbreak.

Any time we find listeria in food, we would consider that food adulterated and ask for a recall, Karas said.

He said the finding of listeria in romaine lettuce resulted from an FDA research program to understand the prevalence of listeria in fresh produce, particularly lettuce and leafy greens.

The recall is already the fourth since Jensen Farms voluntarily recalled cantaloupes linked to the outbreak on Sept. 14. Only one of the four subsequent recalls -- of cantaloupes by Kansas food processor Carol's Cuts LLC -- was related to the outbreak.

True Leaf Farms, a processing arm of Salinas, California-based Church Brothers LLC, originally said in a release on Friday that it was voluntarily recalling 90 cartons of romaine shipped from Sept. 12-13 to a food service distributor in Oregon, who sent it to at least two other states, Washington and Idaho.

Later on Friday, the company expanded the recall to 2,498 cartons of chopped or shredded romaine shipped to 19 states and Canada. On average, each carton has six bags.

We don't know where the problem is. It could have been from the field, it could have been from the plant, Church Brothers Chief Executive Steve Church told Reuters.

He said the FDA visited the company's plant on Thursday and planned to return next week. The recall stemmed from a random check of a sample from a single bag.

Church said the company was working closely with the FDA.

The 2-pound (0.9-kg) bags of romaine lettuce affected by the recall have a Sept. 29 use-by date.

Listeria rarely causes serious illness. For it to do so, the organism needs to get on the food and grow to levels where it can cause disease. Since it can grow at low temperatures, that can happen anywhere along the food chain.

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