Pregnant women, young children, and the elderly are especially susceptible to severe Listeria infections.
Infections linked to packaged salads from 2 different firms caused 30 illnesses.
Seven new illnesses and 2 additional deaths have been confirmed in the outbreak, which has grown to 27 cases and 6 deaths.
Twenty people in 15 states have been now sickened in the outbreak, and 4 have died.
The CDC's FoodNet program has reduced required surveillance from 8 foodborne pathogens to 2, a move some experts warn could leave the country more vulnerable to outbreaks.
So far 40 states have reported measles cases, with 88% of infections part of 29 outbreaks.
A pregnant woman who was sickened has also reported fetal loss following her infection.
An earlier investigation hinted at hospital food as a source, but evidence didn't reveal a specific item.
FDA and USDA teams are still working to identify a food source for the Listeria outbreak.
Illnesses have been occurring since 2018, mainly in nursing home residents, with the latest cases reported this year.
