While eating leafy greens is good for you, there is also a flip side to that as well according to the Center for Disease Control and Prevention.

When Donna McKay shops for produce, she said she selects the fresh, unprocessed stuff.

"And I don't really want the pre-washed because I end up having to wash it anyway," she said.

McKay said she is careful because of past reports linking tainted spinach to food poisoning.

Now, a CDC study shows dramatic increases in foodborne illness from eating the greens.

According to the research, people getting sick after eating greens rose 60 percent from 1986 to 1995. From 1996 through 2005, those illnesses rose 39 percent.

The most common illness reported was from the norovirus, which triggers the stomach flu.

Researchers say they don't know the direct cause, but tests ordered by News 8 in 2006 showed that even pre-washed lettuce and spinach contain high amounts of bacteria.

Dallas County health inspector Betty Gray said opportunity for food poisoning lurks in processing from the moment veggies are harvested.

"We have the possibility of the human hand touching it, the machinery touching it [and] the bagging process," Gray said. "There are many processes where the food is exposed to elements that could cause a contamination."

There is one way to prevent food-borne illness when preparing a salad, which is wash the greens even when the package claims they're already clean. The same rule applies to those convenient, pre-cut fruits.

E-mail jstjames@wfaa.com