Colorado State University Extension
SafeFood Rapid Response Network
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SALAD GREENS: KEEPING E. COLI OUT OF THE MIX
Edited by: Stephanie Wallner, M.S., Mary Schroeder, M.S., R.D, Pat Kendall, Ph.D., R.D., Colorado State - Winter 2007
Highly publicized outbreaks of foodborne illness linked to spinach and lettuce in recent months have raised public awareness and caused consumer anxiety regarding the safety of popular salad greens. Last September, an outbreak of E. coli O157:H7 infection across more than 20 states prompted grocers and retailers to pull bagged spinach from their shelves, causing a scare among those who use conveniently pre-packaged spinach at home. According to the U.S. Food and Drug Administration (FDA), this outbreak affected 26 states, with 204 confirmed illnesses caused by E. coli infection, some quite severe. Three victims died, and 31 cases progressed to hemolytic uremic syndrome, a serious E. coli-related condition that often results in kidney failure.
Only weeks following the spinach scare, fresh lettuce was implicated in an E. coli outbreak affecting people in seven states. In late 2006, yet another fresh produce-related outbreak of E. coli infection was linked to Taco Bell restaurants in Pennsylvania, New Jersey, New York, Delaware, and South Carolina. By year's end, 71 confirmed cases in these 5 states were linked to lettuce from Taco Bell restaurants. During the outbreaks, pre-packaged spinach and salad mixes were temporarily removed from grocery store shelves, and consumers were urged to avoid fresh spinach and some lettuce until the FDA determined these products safe to eat.
Although E. coli contamination traditionally has been associated with undercooked meats such as ground beef, it can be very problematic in fresh produce, such as spinach, lettuce, and raw sprouts, and in unpasteurized juices as well. The recent spinach outbreak was the 20th such episode of foodborne illness caused by spinach or lettuce since 1995. The main symptom of E. coli infection is diarrhea, often with bloody stools and accompanied by stomach cramps. For most healthy people, illness clears up on its own, but for children, the elderly, and others with compromised immune systems, infection can result in kidney failure and even death.
Pre-packaged greens and salad mixes have become increasingly popular for both convenience and, ironically, safety reasons, and now make up 80% of the lettuce and spinach market. However, the production process can be a source of contamination. When greens are cut in the field rather than left whole, the outer, protective layers are discarded, steps which can introduce contamination. In addition, potentially contaminated greens can be mixed with clean ones during packaging. Finally, although packages are often labeled with the reassuring phrase "triple-washed," the pre-washing procedures used are not 100% effective in eliminating all contaminants, even when done correctly. Therefore, consumers are at risk of eating contaminated greens while assuming that bagged, "pre-washed" produce mixes are safe.
Experts have differing opinions about the effectiveness of washing bagged greens at home before use. Some believe that harmful bacteria may be too deep in the crevices or leaves of greens for re-washing to be effective. According to Scientific Certification Systems, a company that audits industry practices, washing at home removes only 60-90% of microbes on produce surfaces. In addition, supermarket produce washes are thought to be minimally effective and work only as well as tap water. Other experts suggest that it can't hurt to rinse greens from pre-washed packages as an extra safety measure, provided that kitchen surfaces and hands are clean.
The only sure way to destroy bacteria on produce such as spinach is by cooking or boiling, although this isn't an appetizing option for lettuce. Spinach and other greens must be cooked at 160 degrees F for at least 15 seconds in order to kill bacteria. If microwaved, the food should be stirred part way through cooking to help evenly distribute heat. For uncooked greens, purchasing fresh, unpackaged greens may be a better option than pre-packaged mixes. Removing the outer leaves from heads of leafy greens can help to remove bacteria, although this step should also be followed by a thorough rinse under running water. For now, consumers are not being advised to stop eating salad greens, but should follow handling precautions recommended by the FDA and Centers for Disease Control and Prevention (CDC) to help avoid foodborne illness from these foods. For uncooked greens, the following selection and handing tips are recommended:
- Buy only fresh-cut produce and bagged salads if refrigerated or surrounded by ice.
- Place lettuce and other raw fruits and vegetables in bags and keep separated from raw animal products.
- Store perishable fresh fruits and vegetables (like strawberries, lettuce and mushrooms) or pre-cut or peeled produce in a clean refrigerator at 40ºF or below.
- Wash fruits and vegetables under running water just before eating, cutting or cooking, even if you plan to peel them.
- Scrub firm produce, like melons and cucumbers, with a clean produce brush. Let air dry before cutting.
Sources:
- United States Food and Drug Administration Website. Nationwide E. Coli O157:H7 Oubreak: Questions and Answers. Available at: http://www.cfsan.fda.gov/~dms/spinacqa.html.
- United States Centers for Disease Control and Prevention Website. Multi-State Outbreak of E. coli O157:H7 Infections from Spinach. Available at: http://www.cdc.gov/ecoli/2006/September/.
- Tufts University Health & Nutrition Letter, December 2006, pp. 1-3.
- United States Centers for Disease Control and Prevention Website. Multistate Outbreak of E. coli O157:H7 Infections, November-December 2006. Available at: http://www.cdc.gov/ecoli/2006/december/121406.htm.
