(UPDATED COVERAGE, Sept. 16, 4:33 p.m.) Shredded lettuce is taking the blame for sickening 124 people across the U.S., primarily in Western states, and 12 in Canada with salmonella this summer.
Bill Keene, senior epidemiologist for The Oregon Public Health Division, said shredded lettuce, possibly from quick-service restaurant locations, is the likely cause of a Salmonella typhimurium outbreak that started mid-July, peaked in August, and tapered off later that month.
Keene has been involved in the epidemiological traceback for weeks, he said, and recently saw the investigation mostly handed over to the Food and Drug Administration and state departments of agriculture, as shredded lettuce seems to be a fairly common denominator for affected people.
"FDA launched its involvement around the first of September," said Sebastian Cianci, spokesman for the FDA. "So far we have not been able to identify a vehicle of transmission, so we don't know a vehicle yet, but we do believe it's food related."
There were no lettuce recalls associated with this outbreak, which makes the investigation difficult. Any contaminated product would have been consumed by now, Keene said, so traceback cannot be confirmed by testing.
Consumer reports of food consumption are being used as primary evidence, along with invoices and shipping and receiving records from restaurants, distributors and shippers.
Cianci said the outlet for the unconfirmed source of contamination seems to be fast food restaurants, although not necessarily chain restaurants.
"People reported eating at one or more fast food restaurants, often multiple restaurants," Cianci said. "But it doesn't seem to be one restaurant chain or one type of food served. And it does not seem to be associated with food sold at grocery stores."
There are still a few loose ends to tie up in epidemiological testing, Keene said.
“The epidemiological evidence can be confirmatory, and that’s what’s still in progress,” Keene said. “There still is work to be done to rule out other possibilities. But it’s fair to say that most people say this is the one.”
Although Keene and a portion of his colleagues are convinced, authorities hesitate to convict shredded lettuce, partly in light of false allegations against tomatoes during the Salmonella Saintpaul outbreak in 2008.
“I don’t think anyone’s still arguing it’s something else, but some say the evidence isn’t quite there,” Keene said. “People are understandably and appropriately reluctant to cross the ‘T’s and dot the ‘I’s before all the evidence is in.”