A lettuce farm in Santa Barbara County, California, has been linked to an E. coli outbreak that has sickened 59 people in 15 states.

The U.S. Food and Drug Administration announced Dec. 13 that a positive sample result for the same strain of E. coli connected to the outbreak was found in the sediment of a local irrigation reservoir used by a single farm owned and operated by Adam Bros. Farms.

The FDA said it will send investigators back to this farm for further sampling.

“It’s important to note that although this is an important piece of information, the finding on this farm doesn’t explain all illnesses and our traceback investigation will continue as we narrow down what commonalities this farm may have with other farms that are part of our investigation,” FDA commissioner Scott Gottlieb said in a statement. “While the analysis of the strain found in the people who got ill and the sediment in one of this farm’s water sources is a genetic match, our traceback work suggests that additional romaine lettuce shipped from other farms could also likely be implicated in the outbreak.”

The water from the reservoir on this single farm, he added, doesn’t fully explain what the common source of the contamination is.

While the new information does not fully explain the outbreak, it does allow the FDA to revise its recommendations for consumers slightly, Gottlieb said.

“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.”