guest columnist / editorial / opinion
Lessons from the spinach patch: the recent E. coli O157:H7 outbreak

Kathryn Boor is a professor of food science and serves as director of the Milk Quality Improvement Program at Cornell University. She contributes this column exclusively for Cheese Market News.

Events moved quickly with the August/September 2006 Escherichia coli O157:H7 outbreak associated with spinach. On Sept. 8, 2006, Wisconsin public health officials reported a cluster of E. coli O157:H7 infections to the Centers for Disease Control and Prevention (CDC). On Sept. 12, the CDC confirmed that the E. coli O157:H7 strains from Wisconsin yielded pulsed-field gel electrophoresis (PFGE) patterns (“fingerprints”) that matched those from isolates recently-submitted from other states. This information suggested the same strain of this deadly bacterium was surfacing simultaneously at multiple locations around the country, signaling an early phase of a multi-state foodborne illness outbreak.

On Sept. 13, 2006, epidemiologists in Wisconsin and Oregon informed CDC officials that they suspected fresh spinach as a possible source of E. coli O157:H7 infection clusters that had been observed in both states. Epidemiologists in New Mexico also reported a cluster of infections associated with spinach consumption on the same day. On Sept. 14, FDA used press releases and a press conference to advise consumers not to eat bagged fresh spinach, which was rapidly followed on Sept. 15 by a voluntary recall of all fresh spinach-containing products by one California company.

The next day, FDA advised consumers to avoid eating any fresh spinach or spinach-containing products. Then on Sept. 21, FDA officials announced they had localized the source of the outbreak to spinach grown in three California counties (Monterey, San Benito and Santa Clara counties). By Sept. 26, a total of 183 people from 26 states were reported to the CDC as infected with the same strain of E. coli O157:H7, suggesting that they had become ill from consuming the same contaminated food product. Of these, 95 were hospitalized, 29 developed hemolytic uremic syndrome (HUS) and 1 died.

E. coli O157:H7 with PFGE patterns matching those of the patients were isolated from 3 open packages of fresh spinach that had been consumed by patients (one in New Mexico, one in Utah and one in Pennsylvania). It is very likely that the rapid identification of spinach as the source of E. coli O157:H7 exposure and the removal of contaminated products from store shelves helped prevent additional illnesses and saved lives.

While all foodborne illness outbreaks garner attention, E. coli O157:H7 outbreaks make headlines because of the severity of illnesses associated with this organism. E. coli O157:H7 was first recognized as a human pathogen in 1982, following an outbreak of bloody diarrhea associated with consumption of undercooked hamburgers. Illness symptoms generally emerge between 2 to 8 days after consumption of E. coli O157:H7-contaminated foods. The infection typically causes severe bloody diarrhea and abdominal cramps, usually with little or no fever. The majority of those infected recover in 5-10 days.

For some people, however — particularly for children under 5 years of age and the elderly — the infection can result in development of HUS, characterized by kidney failure and destruction of red blood cells. HUS occurs in about 8 percent of those diagnosed with the infection. In the United States, HUS is the principal cause of acute kidney failure in children, with the majority of cases resulting from E. coli O157:H7 infection.

How did the spinach become contaminated? This important question still is under investigation. According to Robert Brackett, director of FDA’s Center for Food Safety and Applied Nutrition, a joint FDA/State of California field investigation still is ongoing. The investigative team, which also has included experts from CDC and USDA, has inspected facilities and collected samples from the environment and water associated with the spinach operations. The same strain of E. coli O157:H7 that was involved in the illness outbreak was also isolated from water samples taken from a stream as well as from fecal samples obtained from cattle and wild pigs. It is likely that wild pigs had gained physical access to the spinach fields.

Animal manure is an important source of this organism. The fact that E. coli O157:H7 has been isolated from the intestines of healthy cattle, deer, sheep and goats, among others, highlights the critical need to ensure the absence of fecal material from foods that will not be cooked prior to consumption as washing alone will not ensure removal of all bacterial contaminants from fresh produce.

In the United States, E. coli O157:H7 infections have been linked to consumption of sprouts, lettuce, salami, juice and unpasteurized milk, as well as with swimming in or drinking sewage-contaminated water. In fact, 4 people in California and 2 people in Washington State who reported consumption of raw milk also became ill in September 2006. The E. coli O157:H7 strain obtained from these patients did not match the spinach strain, suggesting that they were not part of the larger spinach outbreak.

The take-home message from these illnesses is that ready-to-eat fresh vegetables, fruits and prepared salads have a high potential risk of bacterial contamination because they are typically grown outdoors in a field or orchard and they are usually consumed without cooking or an equivalent treatment (e.g., pasteurization) that could eliminate pathogens that may be present. Raw milk has a similar risk profile. Every step from the farm to the dinner table – from growth, harvest, packaging and processing to distribution and service — all affect the safety of these products.

Natural Selection Foods, the company whose products were associated with the spinach outbreak, now has implemented a number of measures designed to “raise the bar” on food safety, including testing of all freshly-harvested greens prior to entry into their production stream, as well as an aggressive plan for working with their growers “from seed to harvest.” However, the consumer also has responsibility for ensuring the safety of foods served at their own tables. Foodborne illness risks for the most vulnerable in our population (children under 5 years of age, the immunocom-promised and the elderly) can be reduced by consuming cooked vegetables and peeled fruits, ensuring that ground beef products are thoroughly cooked (to at least 160oF) and by avoiding consumption of unpasteurized milk, juice and cider.

CMN

The views expressed by CMN’s guest columnists are their own opinions and do not necessarily reflect those of Cheese Market News®.