Leafy greens remain a staple in U.S. grocery carts and restaurant kitchens, but they have also figured prominently in major food-safety investigations over the past decade. Among them, romaine lettuce stands out because it has repeatedly been identified in some of the country’s most serious multistate outbreaks. Federal records and CDC research show the issue is not a single-company event, but a recurring food-safety problem tied to how and where the crop is grown.
The outbreaks that defined the problem
The clearest example came in spring 2018, when a multistate outbreak tied to romaine lettuce from the Yuma growing region in Arizona became the largest leafy-greens-linked STEC O157 outbreak in several decades, according to a CDC report. Investigators identified 240 case-patients in 37 states, with 104 hospitalizations, 28 cases of hemolytic uremic syndrome, and five deaths. The report said 85% of interviewed patients reported eating romaine lettuce in the week before becoming ill.
That outbreak began drawing national attention in April 2018 after New Jersey and Pennsylvania officials reported a cluster of infections associated with multiple locations of a restaurant chain, according to the same CDC report. Product traceback later found that the romaine supplied through several distributors originated in the Yuma growing region. The scale of the illness count and the severity of the complications turned romaine into a national symbol of produce-safety risk.
Romaine was also implicated in later investigations. The FDA said three 2019 outbreaks traced to the Salinas Valley growing region in California collectively sickened 188 people between September and December 2019. In a separate CDC field report on a 2019 outbreak, investigators said traceback linked romaine served at reported restaurant chain locations in California to two common farms, underscoring how frequently the product appears in high-profile investigations.
What the national footprint looked like
The 2018 outbreak stretched across 37 states, making it a truly national event rather than a localized problem, according to CDC findings. The initial cluster was identified in New Jersey and Pennsylvania, but the contamination source was tied back to a major Southwest growing region that ships broadly across the country. That wide distribution is one reason produce outbreaks can expand quickly before investigators isolate a source.
Federal researchers have also documented that romaine appears disproportionately often in multistate leafy-green outbreaks. In a CDC study reviewing U.S. and Canada investigations from 2009 through 2018, romaine accounted for more outbreaks linked to a single lettuce type than any other leafy green. The agency found that among 24 outbreaks linked to one lettuce type, 11 were confirmed, and romaine was confirmed more often than any other variety.
The broader surveillance picture points in the same direction. CDC outbreak summary data for 2017 through 2020 said vegetable row crops were the second most common source of multistate foodborne outbreaks during that period, and romaine was the most common specific leafy green implicated. That does not mean every romaine product is unsafe, but it does show why each new investigation involving the crop draws national scrutiny.
Why romaine keeps showing up
Federal investigators have repeatedly pointed to farm-environment contamination as a central risk. In the 2018 Yuma outbreak, FDA investigators said the most likely route was irrigation canal water after the outbreak strain of E. coli O157:H7 was found in canal water samples. That finding was significant because romaine is typically consumed raw, leaving little opportunity to kill pathogens before it reaches consumers.
In its review of the 2019 Salinas outbreaks, the FDA said adjacent or nearby land used for cattle grazing was the most likely contributing factor. The agency said it could not confirm one definitive source or route, but identified possible indirect transmission of fecal material through runoff, wind, animals, vehicles, or contaminated agricultural water. Those findings show that contamination risks can extend beyond a single field or packing line.
FDA has also described leafy-greens contamination as a longstanding issue. In its fall 2018 investigation summary, the agency said FDA and CDC identified 28 foodborne illness outbreaks with a confirmed or suspected link to leafy greens in the United States between 2009 and 2017. For consumers, the practical reality is that romaine remains widely available and widely eaten, while regulators and growers continue working on water standards, traceback systems, and farm-level controls meant to reduce the risk of another large multistate outbreak.