The U.S. Food and Drug Administration (FDA) has identified a California farm as a possible source of the multistate E. coli outbreak, but it says that the finding on this farm does not explain all illnesses. 

The FDA said investigators had identified the strain of E c.oli causing the current outbreak in a sample collected in the sediment of an irrigation water at a ranch owned and operated by Adam Bros. Farming, in Santa Barbara County.

The strain isolated from this sample matched those collected from ill persons in this outbreak using Whole Genome Sequencing (WGS).

The company hasn’t shipped any romaine since Nov. 20, the FDA said.

Experts are working with the farm to determine how contamination occurred and what corrective actions need to be taken before the next growing season.

"Adams Bros is cooperating with the FDA and CDC in this outbreak investigation. They have committed to recalling products that may have come into contact with water from the water reservoir where the outbreak strain was found," the FDA said.

"The finding on this farm, however, does not explain all illnesses. The FDA’s traceback activities of romaine lettuce will continue as FDA works to determine what commonalities this farm may have with other farms and areas that are being assessed as part of the investigation."

It added that this information allows the FDA to slightly modify its recommendations.

"Given the identification of the outbreak pathogen on the one farm, the location of 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, there is no longer a reason for consumers to avoid romaine from San Luis Obispo, Santa Cruz and Ventura Counties, in California, provided it was harvested after November 23, 2018," it said.

On Dec. 13 Adams Bros announced it is recalling red leaf lettuce, green leaf lettuce and cauliflower harvested on Nov. 27 - 30 "out of an abundance of caution", clarifying that none of the recalled product has tested positive for E. coli.