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Foodborne Disease Outbreaks Associated with Leafy Greens, 1973–2006

K. M. Herman, T. L. Ayers, M. Lynch; Centers for Disease Control and Prevention, Atlanta, GA

Several recent large outbreaks have been associated with leafy green foods in the United States, such as Escherichia coli O157:H7 infections due to spinach; however, the characteristics of all reported outbreaks due to leafy greens have not been described.

The Centers for Disease Control and Prevention conducts surveillance for foodborne disease outbreaks (FBDO) investigated by local and state health departments in the United States.

We reviewed data from the FBDO surveillance system for 1973-2006. A leafy green-associated FBDO is defined as two or more illnesses due to the consumption of a single leafy green food item (lettuce, cabbage, mesclun mix, spinach) or a salad item
containing one or more leafy greens. These data were compared with U.S. leafy greens per capita availability, a proxy for leafy green consumption.

Among 10,421 FBDO reported during 1973-2006, 502 (4.8%) outbreaks, 18,242 (6.5%) illnesses, and 15 (4.0%) deaths were associated with leafy greens. Among leafy green-associated FBDO with a confirmed etiology, Norovirus was responsible for
196 (58.3%) outbreaks, followed by Salmonella, 35 (10.4%) outbreaks, and Escherichia coli O157:H7, 30 (8.9%). The median size of leafy green-associated outbreaks (18 illnesses) was twice the median size of non-leafy green-associated outbreaks (9).

During 1986-1995, U.S. leafy green consumption increased 17.2% from the previous decade. During the same period, the proportion of all FBDO due to leafy greens increased 59.6%. Likewise, during 1996-2005 leafy green consumption increased 9.0% and leafy green associated outbreaks increased 38.6%. In 296 (69.4%) outbreaks, leafy greens were served at a restaurant; 11 (2.2%) involved cases in multiple states.

Conclusions: Leafy greens are an important cause of FBDO and may transmit pathogens with human or animal reservoirs. The proportion of FBDO due to leafy greens has increased, and cannot be accounted for completely by an increase in leafy green consumption. Contaminated leafy greens may cause restaurant-associated or widespread outbreaks.

Efforts by local, state, and federal agencies to control leafy green outbreaks should span from the point of harvest to the point of preparation.

Source: International Conference of Emerging Infectious Diseases 2008

Hmmmm. About the only greens I remember eating as a kid were boiled. Salads, which we did not have often, were anemic affairs of iceberg lettuce, ‘maters, some radishes, onions, and cucumbers. Raw spinach leaves did not comprise a part of our diet. Neither did “organic” veggies grown and packaged a thousand miles away; these were pulled out of the garden.

On the other hand, we had botulism deaths from careless home canning, and “food poisoning” from letting the stuffing sit in the turkey at room temperature for long periods of time. Various digestive maladies were blamed on tainted mayonnaise at church socials and the like.

Perhaps it isn’t so much that leafy greens are more contaminated than before but that contaminated foods are not limited to one family’s garden, but are instead disseminated throughout the United States via shipping to nationwide grocery stores and restaurants.

I also believe that there is a strong likelihood that the various bacterial diseases were not recognized and/or tracked earlier for what they were but were instead blamed on a viral “stomach flu”.