After extensive research into California supply chain farms, water irrigation systems, and history of previous E.Coli outbreaks, the U.S. Food and Drug Administration (FDA) along with the U.S. Centers for Disease Control Prevention,were able to trace the November 2018 E. Coli outbreak to a farm in Santa Maria, California in December. According toa press release from the FDA, though, the finding didn't end the investigation.

Commissioner Scott Gottlieb said in the release that, "the most likely way romaine lettuce on a specific ranch on this farm became contaminated was from the use of water from this reservoir as agricultural water. It is believed that this water came into contact with the harvested portion of the romaine lettuce, since the outbreak strain of E. coli O157:H7 was found in sediment from the reservoir and in no other sampled locations."

However, Dr. Gottlieb and the FDA doubt that the contamination from one farm could explain the entire outbreak.

Even on a farm with procedures in place to collect, test and sanitize reservoir water before use, verified procedure records were not available.

"The finding of the outbreak strain in the sediment of the water reservoir is significant, as studies have shown that generic E. coli can survive in sediments much longer than in the overlying water," noted Dr. Gottlieb. The E. Coli bacteria was likely present in the on-farm reservoir for months or years before a positive sample was found.

Further, the FDA found evidence of many wild animals in the vicinity of the reservoir which could have contributed to the outbreak.

It’s important to understand where leafy greens are grown and harvested and not simply the location of the business entity that shipped or processed the produce, Dr. Gottlieb said in his statement.

To prevent future outbreaks and illnesses, the FDA recommends producers of leafy greens to provide an easily traceable packaging, origin of product and time and date of harvest.

The FDA concludes that "without the ability to identify the growing region or specific suppliers of suspected shipments, the public messages issued by the FDA and other public health partners during recalls or outbreaks will continue to be--out of necessity--broad and likely to include farms and growing regions that may not be responsible for the contamination."