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.