Although v oluntary recalls have removed what the Centers for Disease Control identified as listeria-contaminated cantaloupe from the shelves, the numbers of illnesses and deaths continue to climb. According to the CDC’s most recent numbers, 123 people have been infected with one of the four outbreak-associated strains of Listeria monocytogenes and 25 have died, up from the 18 deaths reported as of Oct. 4.

Pennsylvania has now reported its first illness, making it the 26th state to report an illness, the CDC reported Tuesday.

Jensen Farms in California and Kansas food processor Carol’s Cuts – two suspected sources of the outbreak – voluntarily recalled their cantaloupes back in September, so why do the cases of listeria continue to mount?

It has to do with the incubation of the illness. Someone who ate contaminated food might not develop listeriosis, the infection associated with the listeria bacteria, until months later.

“More ill persons may be reported because of the time lag between diagnosis and laboratory confirmation and also because up to two months can elapse between eating contaminated food and developing listeriosis,” the CDC wrote in an investigation update Tuesday.

Older adults, people with weakened immune systems, pregnant women and newborns are most at risk for developing listeriosis and anyone who thinks they have become ill from eating contaminated cantaloupes should consult their doctor immediately, the CDC wrote.

The CDC provides tips for reducing one’s risk of listeria from cantaloupe and other foods here.