The Public Health Agency of Canada advises consumers to follow safe food handling tips when preparing lettuce. Unwashed lettuce, including whole heads of lettuce sold in sealed bags, should be handled and washed using these steps:
Discard outer leaves of lettuce.
Wash unpackaged lettuce under fresh, cool running water. There is no need to use produce cleansers — washing lettuce gently with water is equally effective.
Keep rinsing lettuce until all dirt has been washed away.
Don’t soak lettuce in a sink full of water. It can become contaminated by bacteria in the sink.
Store lettuce in the refrigerator for up to seven days. Discard when leaves become wilted or brown.
Use warm water and soap to thoroughly wash all utensils, countertops, cutting boards and storage containers before and after handling lettuce to avoid cross-contamination.