The U.S. Food and Drug Administration and the U.S. Centers for Disease Control and Prevention acted quickly to protect consumers from an emerging outbreak of E.coli O157:H7 linked to romaine lettuce by issuing a public warning this past November and recommending that industry and retailers voluntarily remove the product from the market. It was critical to provide this advice because it was believed that contaminated produce was still in the food supply at a time when Americans were preparing meals to celebrate Thanksgiving. By removing potentially contaminated products from the market, health officials and industry were able to reduce additional illnesses.
Evidence at the beginning of this outbreak showed that the genetic fingerprint of the pathogen obtained from patients impacted by the 2018 outbreak was similar to the strains associated with an outbreak previously linked to leafy greens in 2017. With help from this historic information, our staff worked quickly to initiate traceback from points of sale through the supply chain ultimately to the farms where the romaine could have been grown. Investigators were able to narrow down the growing region to California based on trends in the industry. Moreover, the supply chain pointed to specific California counties.
The traceback investigation identified multiple farms that may have been implicated in this outbreak. These farms became the focus of further evaluation. The FDA led a team of experienced federal and state investigators who were tasked with taking samples and inspecting these farms to try and find out where and how this outbreak happened. They collected samples of soil, animal feces, fertilizer, agricultural water and reservoir sediment. The CDC was able to find one positive match to the outbreak strain in the sediment of an on-farm water reservoir, used for irrigation, in Santa Maria, Calif.
The investigation teams made numerous visits to leafy greens farms in various counties and growing regions of California identified through traceback. The outbreak strain of E. coli O157:H7 was not detected in any other samples collected during this investigation. On December 17, 2018, the farm with the positive match to the outbreak strain in the sediment issued a recall of romaine lettuce and other products -- including red leaf lettuce, green leaf lettuce and cauliflower -- that may have also been contaminated due to use of agricultural water from the on-farm reservoir.
Given the critical nature of these activities, during the partial lapse in funding, the FDA and CDC continued work on this investigation. Thanks to this continued effort during the partial funding lapse, we were able to declare the outbreak over – just over two months after it was first announced – once we were confident that contaminated product could no longer be available for purchase and there were no new illnesses linked to romaine from the implicated California growing areas. Even though the outbreak was declared over, the FDA’s investigation continued. We wanted to understand the factors that allowed this outbreak to happen and provide information to help prevent similar outbreaks from occurring again.
Today, we’re announcing the findings of this investigation and our best hypotheses as to how this contamination could have occurred. In the case of the one farm with a positive sample previously referenced, the FDA believes 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. The water from the reservoir doesn’t explain how lettuce grown on other ranches or farms identified by traceback may have been contaminated. So, this one farm cannot explain the entire outbreak.
As part of our investigation, we determined that the farm had a procedure in place to collect and test reservoir agricultural water for generic E. coli and to treat the agricultural water with a sanitizer before use. However, the investigation team noted the verification procedure records did not document that sufficient sanitizer was present to adequately reduce any pathogens present in the water when this water was used for direct contact with romaine lettuce at harvest, during postharvest handling, and to wash/rinse harvest equipment food contact surfaces. It’s important to note that the farm reported that it did not use water from the reservoir for the dilution of crop protection chemicals. It also remains uncertain how the outbreak strain of E. coli O157:H7 was introduced into their on-farm water reservoir.
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. It’s possible that the outbreak strain may have been present in the on-farm water reservoir for some months or even years before the investigation team collected the positive sample. It is also possible that the outbreak strain may have been repeatedly introduced into the reservoir from an unknown source.
The teams did find evidence of extensive wild animal activity, including waterfowl, rodents, coyotes, etc., and animal burrows near the contaminated reservoir. This likely warrants consideration as a possible source of the human pathogen found in the on-farm water reservoir. It is another factor that we will work with the farm to address. Additionally, adjacent land use including the use of soil amendments, or for animal grazing on nearby land, may have had the potential to be contributing factors.
As explained in the Environmental Assessment of Factors Potentially Contributing to the Contamination of Romaine Lettuce Implicated in a Multi-State Outbreak of E. coli O157:H7, which provides the findings of the unrelated spring 2018 investigation into contamination that originated in the Yuma growing region, food safety problems related to raw whole and fresh-cut (e.g. bagged salad) leafy greens are a longstanding issue. The FDA and CDC identified 29 foodborne illness outbreaks of Shiga-toxin producing E. coli (STEC) with a confirmed or suspected link to leafy greens in the United States between 2009 and 2017. STEC contamination of leafy greens has been identified by past investigations, traceback, observation and sample collection results as most likely to occur in the farm environment.
To help ensure that leafy greens are safe and mitigate problems that might occur, 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. It’s also important to be able to determine which farms and growing regions are responsible for supplying the contaminated product and the time frame when product was supplied. This information is crucial to the development of accurate public health messages to both protect consumers from exposure and empower retailers and consumers to take appropriate actions.
The FDA continues to recommend that leafy green growers, buyer/shippers and retailers be able to trace product back to the specific source in real time and make information about the source, such as harvest date and standardized growing regions, readily available for consumers on either packaging or point of sale signs, or by other means. We’re pleased to see many companies in the leafy green industry take voluntary steps to quickly respond to our previous recommendations. We believe this is the best approach to be able to inform consumers should there be any future risks to public health. Our first goal is working with federal, state and industry partners on implementing best practices to try and prevent these outbreaks in the first place. But when outbreaks occur, 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. We know more needs to be done and there is a shared sense of urgency around these efforts.
The FDA recommendations based on this investigation are similar to, and reinforce, the changes recommended for the leafy green industry in the Yuma environmental assessment. We continue to strongly recommend that all segments of the leafy greens industry thoroughly review current operations, procedures, policies and practices taking into consideration the findings of this investigation report, the FSMA Produce Safety Rule, the FSMA Preventive Controls for Human Foods Rule and other relevant FSMA regulations. Other available science-based information relevant to the reduction or elimination of human pathogens on leafy greens should also be considered. In addition, industry should make the necessary modifications to operations, procedures, policies and practices to ensure safe products for consumers and minimize the likelihood of similar outbreaks in the future.
We’ll continue to work with industry to explore better ways to assure quick, accurate and easy access to key traceability information. The FDA believes that widespread industry adoption of existing and emerging technologies, which can be used to trace product from the field to the consumer in real time, is a critical piece of our ability to protect the public. In addition, the agency has already started special, microbiological surveillance sampling assignments for romaine lettuce that is grown for distribution throughout the country. If samples are found to be contaminated, the FDA will follow-up with the responsible farms and firms to assure that they remove contaminated products from the market. The agency will also work with responsible farms to determine issues and identify steps they can put in place to prevent contamination in the future.
Advancing the safety of fresh leafy greens requires ongoing collaboration. We urge all segments of this industry, from farm to table, and our government partners to review the findings of our investigation and make necessary changes. We recognize and appreciate the efforts that the leafy greens industry has taken to date. But together, we also know more must be done on all fronts to help prevent future foodborne illness outbreaks. We remain committed to further strengthening the FDA’s food program and applying our food safety expertise as we work to better safeguard the U.S. food supply.
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