Per a Michigan State University Press Release, bagged salads might be a gamble not worth taking. Think of bagged salads as a game of chance – one in which the odds are stacked against you.

Prewashed packaged vegetables, like the spinach that is the focus of the recent outbreak of E. coli, always have been viewed with suspicion from experts in foodborne illness because it’s a packaging system that inherently increases the risk of spreading germs.

Thomas Whittam, Michigan State University Hannah Distinguished Professor of microbial evolution, said the combination of E. coli’s durability and power – as few as 10 cells can cause illness – with a mixture of produce creates the potential for a veritable stew of food poisoning. 

E. coli sticks well to plants and doesn’t wash off. Buying individual bunches or heads of greens minimizes the chances of contamination.

"When a contaminated plant gets mixed in with hundreds of other plants and packaged together, and when it takes very few bacteria to get sick, that really increases the risks," Whittam said. "With washing you can remove 99.99 percent of the bacteria, but the few that make it through don’t get killed by normal defenses in the stomach."

"Basically, you’re assuming a lot of risk." Whittam’s Microbial Evolution Laboratory at MSU explores the genetic and adaptive changes underlying the origin and spread of new pathogenic bacteria, including work on new strains of E. coli to try to keep ahead of what may be the next outbreak.