The discovery of E. coli in Salinas Valley irrigation water used on a lettuce crop indicates that fecal bacteria is widespread in the environment but offers no new insight into the contaminated spinach that has sickened nearly 200 people, food safety experts said Monday.
Nunes Co. of Salinas, Calif., voluntarily recalled more than 8,500 cartons of green-leaf lettuce Sunday after discovering E. coli in irrigation water used on the crop. The water came from a farm's deep wells but had been stored in a reservoir before it was pumped into the farm's irrigation system.
Most E. coli bacteria are not harmful to humans and, in fact, are found in the stomachs of people as well as other mammals and birds. The bacterium identified in the lettuce irrigation water was this generic form of E. coli, which is common in water and soil around the world.
Further testing will show whether the water also contained a virulent strain of E. coli, known as O157:H7, that sickened people who ate spinach grown in the Salinas Valley, Food and Drug Administration officials said. Of 199 people who fell ill in the spinach outbreak, 102 were hospitalized and three died.
The type of E. coli in the water used on the recalled lettuce is found in the feces of every warm-blooded animal, said Dean Cliver, a food safety professor at UC Davis. "It typically does no harm but is used as an indicator of fecal contamination," Cliver said. "Unless it was present in unusually high levels, it probably did not indicate a threat to consumer health."
Water from that reservoir apparently does not share a common source with water supplies used on the region's spinach and other crops.
"Currently there is no link between the Nunes Co. and the previous spinach outbreak," said David Acheson, chief medical officer at the FDA's food safety center.
Food safety experts say Nunes Co.'s recall indicates growers in the region are being very cautious in light of the spinach outbreak.
Acheson praised the company for taking preventive action and recalling the lettuce despite the lack of evidence of a health threat. "We do not have an outbreak. We have a recall of lettuce that may be contaminated with generic E. coli," Acheson said.
"At this stage we don't know whether the E. coli found in the irrigation water contains any harmful E. coli to humans," he added.
By Monday morning, all but 250 cartons of the lettuce sold under the Foxy brand between Oct. 3 and Oct. 6 had been found and were being destroyed, company President Tom Nunes said. The search continued for the remaining cartons, which were believed to be in supermarkets or restaurants in Arizona, California, Nevada, Washington, Oregon, Idaho and Montana. Nunes Co. grows more than 20,000 acres of vegetables in Arizona and California.
In the spinach investigation, researchers still have not pinned down the source of the E. coli O157:H7 in the product distributed by Natural Selection Foods of San Juan Bautista, Calif.
Nevertheless, many microbiologists suspect that it originated in the fields and that water is a likely route of transmission.
In the case of the lettuce, Acheson said, investigators will be especially interested in learning whether the irrigation water was tainted by "a few E. coli or whether there was a load of them." If there is a lot, it is a sign of major contamination by fecal matter that could contain human pathogens.
"Part of the ongoing investigation is to ask these kinds of questions. Is this a new phenomenon? What's the extent of E. coli contamination in the irrigation water?" he said. "It's premature to point the finger at irrigation water and say it is the problem.... It's something clearly that is being looked at, and it could be part of the problem."
Trevor Suslow, a UC Davis plant pathologist who focuses on safety of fresh produce, has sampled 19 reservoirs in the Salinas Valley over the last few years. Roughly "one in five samples had detectable nonpathogenic E. coli," he said.
But, he said, "it's a very different situation than the situation with the spinach."
Nunes Co., he said, showed "an abundance of caution" in recalling its lettuce because "finding nonpathogenic E. coli in water sources used for irrigation is not that uncommon and it's not really, in and of itself, reason for great alarm."
"This recall was very much in response to a heightened sensitivity by the industry given where we've been these last three weeks," said Tom Stenzel, president of the United Fresh Fruit and Vegetable Assn., based in Washington, D.C. "That grower-packer was being extremely cautious.... What I'd tell my family is that it's actually a cause for comfort that the industry would do that, knowing it would cause anxiety again."