Because their leaves are delicate and they're grown in open fields, leafy greens are susceptible to contamination.
On the farm, bacteria can come from animal waste that washes into fields and irrigation canals.
In the processing plant, contaminated lettuce that's chopped and bagged can spread bacteria further.
"We don't want people to use this as an excuse to stop eating fresh fruits and vegetables," says Kevin Loria. "Leafy greens, like lettuces, spinach, kale and arugula, are loaded with vitamins and nutrients."
For the average person, the chances of getting sick from leafy greens are extremely low.
Consumer Reports has some steps you can take to further decrease your chances of getting sick.
Consider buying whole heads of lettuce. The inner leaves are often cleaner and are not handled as much as lettuce that comes in bags. That could reduce the chances of the product being contaminated.
Keep packaged lettuce cold. Bacteria multiplies at room temperature.
"Only buy what you're going to eat fresh," Loria said. "If you see damaged leaves or bruised or slimy greens in the package, don't eat from that."
Consider hydroponic or greenhouse-grown greens as they may be less likely to be contaminated by animal waste.
Research shows that soaking greens in a vinegar and water solution for 10 minutes can reduce bacteria levels.
Finally, cooking sturdier greens until they're soft in this best bet to reduce your risk of food poisoning.
Consumer Watch: How to keep your leafy greens clean