A farm near Yuma, Ariz., has been identified as a suspected source of E. coli bacteria in an outbreak that has sickened scores of people in 22 states.
But federal health officials cautioned Friday that only eight of 98 cases were traced to the farm's romaine lettuce and that two dozen other sites in Arizona remain under investigation.
Harrison Farms, located about two miles from the California border, supplied whole-head romaine lettuce to a correctional facility in Nome, Alaska, where eight inmates were sickened, the Centers for Disease Control and Prevention said. Harrison Farms officials were not immediately available for comment.
No recall has been issued because romaine from Harrison's fields, which was harvested from March 5-16, has exceeded its 21-day shelf life and has either been consumed or thrown away, officials said. "Harrison Farms has ceased production of lettuce — they're growing grass on the field now," said Matthew Wise, deputy branch chief for Outbreak Response at CDC.
Most other growers in the Yuma region have shifted from lettuce to other crops, Wise added.
"We haven't been able to guarantee that there is no product coming out of Yuma at this point, but given the time of year, the expectation is that harvesting has moved north from the Yuma growing region," Wise said.
Dr. Stic Harris, director of the FDA's Coordinated Outbreak Response and Evaluation Network, cautioned that more than two dozen potential contamination sources in the Yuma region remain under scrutiny, including fields, packinghouses and other parts of the supply chain.
"It's important to point out that so far we've been able to identify only one specific farm that's responsible for these eight [Alaska] cases, but we still have a lot of work to do to identify other legs of this outbreak," Harris said. "It's difficult for us to say definitively that there's not a continued risk."
FDA spokesman Peter Cassell said all the sites under scrutiny are on the Arizona side of the winter lettuce region, which extends from Yuma County into California's Imperial Valley.
From roughly November through April, these desert regions produce about 90% of the nation's lettuce. Cultivation then begins farther north, including in California's San Joaquin and Salinas valleys, coastal areas, and in other states.
Nonetheless, consumers should continue to avoid Yuma-grown romaine heads or hearts, as well as chopped romaine or salad mixes containing romaine. Any of those products whose source is unknown should be discarded, officials warned.
"This is a serious E. coli." Wise said. "I think everybody should be concerned and everybody should be avoiding romaine."
The CDC on Friday boosted its tally of victims to 98 and added three more states to the map of the outbreak. More cases can be expected due to delays in onset, identification and reporting of illnesses, the CDC warned.
The strain of E. coli has been identified as one that produces strong versions of Shiga toxins, which bind to blood cells and can destroy organ linings — a scenario that has sent 46 people to hospitals, including 10 with kidney failure, the CDC said. That hospitalization rate is far higher than usual, the agency added.
The outbreak is the second worst of its kind since 2006, when about 200 people were sickened by contaminated spinach from the Salinas Valley, the CDC said.
Romaine lettuce has been a relatively common source for bacterial outbreaks, mostly because it is a popular crop that is widely consumed and eaten raw. An outbreak of a different E. coli strain last December killed one person in Canada and sickened 24 others in 15 states.
Here are the warnings the CDC has issued to consumers:
Do not eat or buy romaine lettuce unless you can confirm it is not from the Yuma growing region.
Product labels often do not identify growing regions; so, do not eat or buy romaine lettuce if you do not know where it was grown.
This advice includes whole heads and hearts of romaine, chopped romaine, baby romaine, organic romaine, and salads and salad mixes containing romaine lettuce. If you do not know if the lettuce in a salad mix is romaine, do not eat it.
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4:40 p.m.: This article was updated with additional details and quotes from Center for Disease Control and Prevention and U.S. Food and Drug Administration officials.