They say the investigation is ongoing and more sources are possible, but as of this afternoon, the FDA is reporting traceback efforts in the ongoing E. coli outbreak linked to romaine lettuce has led to Adam Bros. Farm in Santa Maria, CA.

The outbreak strain of E. coli O157H:7 has been confirmed in the sediment of an irrigation reservoir on the family-owned farm, according to officials from the Food and Drug Administration and the Centers for Disease Control and Prevention. During a hastily called news conference today the officials said they can’t yet say the outbreak is over, but it is definitely winding down.

Seven more people have been confirmed infected since the CDC’s Dec. 6 update. Ian Williams, chief of the CDC’s Outbreak Response and Prevention Branch, Division of Foodborne, Waterborne, and Environmental Diseases, said during the news conference that the most recent illness onset date was Nov. 16.

FDA officials said they are continuing to investigate how the E. coli came to be in the sediment of the irrigation pond. They stressed they are also continuing to test samples from other locations.

“As of Dec. 13, our investigation yielded records from five restaurants in four different states that have identified 11 different distributors, nine different growers, and eight different farms as potential sources of contaminated romaine lettuce,” FDA Commissioner Scott Gottlieb said in a statement issued immediately after the news conference. 

“Currently, no single establishment is in common across the investigated supply chains. This indicates that although we have identified a positive sample from one farm to date, the outbreak may not be explained by a single farm, grower, harvester, or distributor.”

Investigators collected samples from the Adam Bros. Farm on Nov. 27, said Stephen Ostroff, senior advisor to the FDA commissioner. The confirmed results from those tests sparked the news conference today.

Ostroff, the CDC’s Williams and two of FDA’s top officials — Deputy Commissioner Frank Yiannas and Kari Irvin, deputy director of the agency’s Coordinated Outbreak Response and evaluation Network — all stressed the investigation is ongoing, with public health epidemiologists continuing to interview patients.

They said the current outbreak is different from the one earlier this year in more than one way. A different strain of E. coli O157: H7 is involved, according to whole genome sequencing. 

Also, the current outbreak strain has not been found in water or sediment that is used by multiple growers. The first outbreak this year, which was associated with romaine from the Yuma, AZ, growing area, has been linked to open water in an open canal that runs between produce fields and a cattle feedlot.

Even though the current outbreak strain has only been confirmed on the Adam Bros. farm, investigators say is it likely additional entities will be implicated. One reason cited for that expectation is the rule of thumb that people generally don’t eat romaine just one time, or from just one source before becoming ill.

The CDC and FDA continue to urge consumers, restaurants, institutional kitchens and retailers to avoid romaine if its origin is not clearly visible on labels. The FDA did, however, remove three California counties from the list of implicated growing areas.

“Given the identification of the outbreak pathogen on the farm in Santa Barbara County, the farms identified in the traceback, and the fact that the lettuce on the market at the peak of the outbreak should be beyond shelf-life we feel there is no longer a reason for consumers to avoid romaine lettuce from San Luis Obispo, Santa Cruz, and Ventura Counties, in California, provided it was harvested after Nov. 23,” according to the FDA. 

“If consumers, retailers, and food service facilities are unable to confirm that romaine lettuce products are from unaffected sources, we urge that these products not be purchased, or if the products have already purchased, they should be discarded or returned to the place of purchase.”

Both FDA and CDC credit the produce industry’s voluntary market withdrawal of romaine two days before Thanksgiving Day as having prevented additional illnesses. Officials say Adams Bros. Farms is cooperating with the FDA, allowing investigators to confirm that the farm hasn’t shipped any romaine lettuce since Nov. 20.