Wash-up from US's romaine lettuce E. coli O157:H7 outbreak

Five died and hundreds were sick following the US’s largest E. coli O157:H7 outbreak in a decade.

It was ultimately established that romaine lettuce irrigated by contaminated canal water in the Yuma region in Arizona was the source of the outbreak. Now the US Food and Drug Administration is looking at the whole incident so that necessary actions to prevent future outbreaks can be put in place and the safety of leafy greens improved.

The FDA is sharing an environmental assessment that details final findings from this investigation. Here are what it has found and decided so far.

One of the investigation’s main objectives was to identify factors that potentially contributed to the introduction and spread of the strain of E. coli O157:H7 that contaminated the romaine lettuce associated with this outbreak. The FDA, the Centers for Disease Control and Prevention and the Arizona Department of Agriculture launched an investigation of the outbreak, leading to the collection of samples in Yuma in order to help gather evidence needed to identify the source of the outbreak.

The environmental assessment confirms the presence of E. coli O157:H7 in three samples of irrigation canal water collected as part of this investigation in the Yuma region. It considers that the most likely way the romaine lettuce became contaminated was from the use of water from the irrigation canal, since the outbreak strain was not found in any of the other samples collected in the region. How the water contaminated the lettuce is uncertain. But based on interviews with growers and pesticide applicators, possible explanations include direct application of irrigation canal water to the lettuce crop or the use of irrigation canal water to dilute crop-protection chemicals applied to the crops through both aerial and land-based spray applications. We cannot rule out other ways the lettuce became contaminated. It’s important to note that we have no evidence that any other product grown in Yuma was contaminated by this water.

How was the canal water contaminated?

When and how the irrigation canal became contaminated with the outbreak strain of E. coli O157:H7 is also uncertain. We know that a large concentrated animal feeding operation (CAFO) is located adjacent to this stretch of the irrigation canal where the samples were collected. This is one potential source. However, the investigation did not identify an obvious route for contamination of the irrigation canal from this facility. In addition, samples collected at the CAFO did not yield E. coli O157:H7. The investigation did not exclude other ways the irrigation canal could have become contaminated with this outbreak strain.

How to prevent another outbreak

The environmental assessment recommends a number of steps that can be taken to reduce the likelihood of another tragic outbreak from occurring in the future.

Fully implementing the Food Safety Modernization Act (FSMA) is critical to these efforts. The FSMA’s Produce Safety Rule must be advanced in collaboration with state regulatory partners and ensure that agricultural water standards work across the incredible diversity of commodities and growing conditions.

Because leafy greens are a highly perishable commodity, the ability to trace back the route of a food product as it moves through the entire supply chain, or traceability, is critical to removing the product from commerce as quickly as possible, preventing additional consumer exposures and properly focusing any recall actions. During the romaine investigation the typical trace-back process was found to be to be particularly challenging because much of the finished lettuce product contained romaine that was sourced from multiple ranches. As a result, the investigation involved collecting documentation from each point in the supply chain to verify the movement of product back to the Yuma area. Complicating this already large-scale investigation, the majority of the records collected in this investigation were either paper or handwritten.

Going forward, both FDA and industry need to explore better ways to standardise record keeping and determine whether the use of additional tools on product packaging could improve traceability.

The FDA is strongly encouraging the leafy greens industry to adopt traceability best practices and state-of-the-art technologies to help assure quick and easy access to key data elements from farm to fork. It is also strongly encouraging the leafy greens industry to explore modern approaches to standardised record keeping and the use of additional tools or labels on product packaging that could improve traceability.

The FDA is exploring ways to best tap into new technologies to significantly reduce the time needed for trace back investigations.

The agency is taking steps to improve its response times and provide actionable information to consumers as quickly as possible. It is also looking at regulatory options and considering appropriate enforcement actions against companies and farms that grow, pack or process fresh lettuce and leafy greens under insanitary conditions. The agency is continuing to explore additional ways to improve these processes and urge all segments of the leafy greens industry to review their operations in the same way.

As a next step, the FDA plans to collect and analyse romaine lettuce samples through a new special surveillance sampling assignment for contamination with human pathogens. This will help us determine whether products are safe to enter the US marketplace. If samples are found to be contaminated, the FDA will follow up with fresh-cut leafy greens processors and their growers or suppliers to determine if these foods were produced under insanitary conditions that render them harmful to consumers and take the appropriate action to remove them from the market.

Whilst recognising and appreciating the efforts that the leafy greens industry has taken to date, the FDA is conscious that more must be done on all fronts to help prevent future foodborne illness outbreaks.

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