Don’t believe the hype on the prewashed lettuce bags you purchase at your local grocery market. Even if the bag looks safe and sealed to the core. Studies have found bad bacteria in these prepackaged bags. See what the professionals have to say.
Don’t assume you can save time by buying the “pre-washed” variety. Studies have found fecal contaminants and other bacteria in bagged lettuce—even those labeled “triple-washed”. So it’s smart to rinse before you eat. It also helps to clean your hands well with soap and water before handling the leaves, and to choose packages with the latest possible “sell by” date.
“The closer to the expiration the more filth we found.” quoted by Urvashi Rangan, Ph.D director of consumer safety at Consumer Reports.
Source: The Shape Guide