FRIDAY, March 23, 2007 (HealthDay News) -- After months of research, U.S. and California health investigators have narrowed the source of last fall's deadly nationwide spinach-borne E. coli outbreak to produce grown in one California field.
But the exact source of the bacteria, which sickened 205 people and killed three, may never be known, health officials have concluded.
"Potential environmental risk factors for E. coli O157:H7 contamination at or near the field [in San Benito County] included the presence of wild pigs, the proximity of irrigation wells used to grow produce for ready-to-eat packaging, and surface waterways exposed to feces from cattle and wildlife," according to a report released Friday by the U.S. Food and Drug Administration, which oversaw the investigation.
"Because the contamination occurred before the start of the investigation, and because of the many ways that E. coli O157:H7 can be transferred -- including animals, humans, and water -- the precise means by which the bacteria spread to the spinach remain unknown," the report concluded.
Beginning early last September, health officials began to receive reports of gastrointestinal sickness after consumption of bagged fresh spinach. On Sept. 15, Natural Selection Foods recalled all of its spinach products with use-by dates of Aug. 17 to Oct. 1. Four other distributors, all of whom got spinach from Natural Selection, also recalled their products.
Natural Selection processes fresh spinach for more than two dozen brands, including Earthbound Farm, Dole and Ready Pac.
The outbreak caused consumers to shun fresh spinach for nearly a month, and the FDA only advised consumers to resume eating the produce again in early October.
Tracing the exact cause of food-borne illness is always tricky, experts said.
Speaking at the height of the outbreak last fall, Dr. Pascal James Imperato, chairman of the department of preventive medicine and community health at SUNY (State University of New York) Downstate Medical Center in New York City, said, "It may very well be that we may never be able to determine whether this occurred in the processing or the growing of spinach."
FDA officials investigated the outbreak with colleagues at the California Food Emergency Response Team (CalFERT), the U.S. Department of Agriculture and the U.S. Centers or Disease Control and Prevention. They say that even though they could not pinpoint the exact source of the bacterium in the tainted spinach, their detective work remains valuable.
"The probe was a notable effort by federal, state and local officials," Robert E. Brackett, director of the FDA's Center for Food Safety and Applied Nutrition, said in a prepared statement. "It yielded valuable information we can use to determine how best to reduce the likelihood of similar outbreaks."
Investigators initially focused their efforts on Natural Selection Foods' processing and packaging plant in San Juan Bautista, Calif., where the contaminated spinach had been processed, the FDA said.
"The next focus of the inquiry was the source of the spinach in 13 bags containing E. coli O157:H7 isolates that had been collected nationwide from sick customers," the agency said. "Using the product codes on the bags, and employing DNA fingerprinting on the bacteria from the bags, the investigators were able to match environmental samples of E. coli O157:H7 from one field to the strain that had caused the outbreak."
Other food-born illness scares have occurred since. Also in September, salmonella-tainted tomatoes caused serious illness in 183 people in 21 states and Canada. And in December, federal health officials traced another E. coli outbreak to iceberg lettuce used in Taco Bell restaurants across the Northeast. That outbreak sickened more than 70 people in five states.
Finally, consumers in February faced a nationwide recall of Peter Pan and Great Value peanut butter implicated in more than 370 cases of salmonella poisoning across 42 states.
Reacting to the slew of outbreaks, U.S. health officials on March 12 released a draft of proposed guidelines for commercial processing of fresh-cut vegetables and fruits.
The voluntary FDA guidelines suggest ways that food industry processors can minimize contamination of ready-to-eat produce by harmful bacteria that are common in the processing of these products.
"The recent outbreaks indicate that clearly more needs to be done to further minimize the risk of food-borne illness," Dr. David W.K. Acheson, director of the Office of Food Defense, Communication and Emergency Response at the FDA's Center for Food Safety and Applied Nutrition, said during an FDA teleconference at the time. "The vast majority of food-borne illnesses are, in theory, preventable."
Consumers can reduce their risk of illness from fresh-cut produce by refrigerating the product after purchase; using clean hands, utensils or dishes in preparing the product; and throwing out the product when the "use by" date has passed, the FDA said.
More information
For more on food-borne illness, visit the FDA.
