The onion-linked Salmonella outbreaks of 2020 and 2021 were not just two large produce outbreaks occurring in back-to-back years. Taken together, they became one of the clearest warnings in recent food-safety history about how vulnerable the fresh-produce system remains to contamination, how difficult traceback can be when widely distributed commodities are involved, and how a humble staple like the onion can become the vehicle for thousands of illnesses across North America. In 2020, a multistate outbreak of Salmonella Newport was linked by some helth agencies to onions from Thomson International in California, ultimately causing 1,127 reported illnesses in the United States and another 515 reported illnesses in Canada. In 2021, a second major outbreak, this time involving Salmonella Oranienburg, was linked to whole fresh onions imported from Chihuahua, Mexico, resulting in 1,040 reported illnesses in 39 states, Washington, D.C., and Puerto Rico. The CDC’s final summary of the 2020 outbreak and the CDC’s final summary of the 2021 outbreak make plain just how large both events were. When two onion outbreaks of that scale happen almost consecutively, the right question is not merely what happened, but what the food-safety system should have learned.
The 2020 outbreak began as a classic modern multistate produce investigation. The FDA’s outbreak page for the 2020 Salmonella Newport investigation explains that the agency, together with CDC and state and local partners, investigated illnesses associated with red onions and later broader onion types. Epidemiologic and traceback information pointed first to red onions as the likely source, but because onions are grown, harvested, packed, and stored in ways that can facilitate cross-contact among varieties, the recall widened to include red, yellow, white, and sweet yellow onions. Thomson International recalled all such onions on August 1, 2020, and the CDC recall archive notes that many additional food products made with recalled onions were subsequently removed from commerce.
What made the 2020 outbreak especially important was not just its size, but the degree to which it showed how an onion problem can rapidly become a supply-chain problem. Onions are not consumed only as loose produce bought one at a time in grocery stores. They move into restaurant kitchens, deli items, meal kits, prepared foods, salsas, sandwiches, dips, and ready-to-eat products. That is why one contaminated onion stream can generate a cascade of secondary recalls. A Food Poisoning News article on the Taylor Farms recall involving products made with recalled Thomson onions illustrates this point well: once the onions were identified, products incorporating them had to be pulled back as well. One of the first lessons of the 2020 outbreak, then, was that a contaminated produce commodity with broad downstream use can create a much wider public-health footprint than consumers may initially realize.
NOTE: In both salmonella onion outbreaks, the law firm of Ron Simon & Associates filed multiple lawsuits.
The 2021 outbreak repeated that lesson on an enormous scale. The FDA’s page on the 2021 Salmonella Oranienburg onion outbreak explains that the investigation identified whole, fresh onions imported from the State of Chihuahua, Mexico, with traceback centering on ProSource Produce and later Keeler Family Farms. The CDC’s final outbreak summary states that the outbreak resulted in 1,040 illnesses and 260 hospitalizations. As in 2020, the problem was not confined to one shelf or one label. Onions had been distributed widely to restaurants, retailers, and food-service operations, and the FDA’s major recalls page for 2021 onion-related recalls documents the breadth of the related product withdrawals.
The first major lesson from comparing the 2020 and 2021 outbreaks is that onions are a high-consequence vehicle when contaminated, even if they are not always thought of that way by the public. Consumers often associate Salmonella with poultry, eggs, peanut butter, or sprouts. Onions do not necessarily sit at the top of the average consumer’s mental list of high-risk foods. Yet these two outbreaks showed that onions can be a near-perfect outbreak vehicle: they are eaten raw or lightly cooked, handled frequently in commercial kitchens, mixed into many foods, difficult to track once chopped or incorporated, and capable of remaining in homes for a long time. The CDC’s 2021 onion outbreak page specifically warned that recalled onions could still be in homes or even freezers because onions have a long shelf life. That long shelf life turns a single contamination event into an extended exposure risk.
The second lesson is that traceback works, but often only after substantial harm has already occurred. In both 2020 and 2021, investigators used a combination of epidemiology, laboratory analysis, and traceback to narrow the source to onions and then to specific supply chains. The CDC’s 2020 updates page and the CDC’s 2021 details page show how public-health recommendations evolved as evidence accumulated. But these investigations also underscore a harder truth: by the time a multistate outbreak is recognized and the traceback picture is sufficiently strong to support recalls and public warnings, contaminated produce has often been widely consumed. Traceback is indispensable, but it is not instantaneous. That means prevention upstream remains more important than response downstream.
The 2020 outbreak produced one of the most concrete post-outbreak analyses. In May 2021, the FDA published its report on factors potentially contributing to contamination of red onions implicated in the summer 2020 Salmonella Newport outbreak. The agency stated that although it could not identify a conclusive root cause, it found several potential contributing factors, including a leading hypothesis that contaminated irrigation water used in a growing field in Holtville, California, may have led to contamination of the onions. That report matters because it shifted the conversation from mere attribution to systems failure. The question ceased to be only “which onions made people sick?” and became “what environmental or agricultural conditions may have allowed contamination to happen in the first place?”
That is the third lesson: irrigation water and the broader agricultural environment remain central vulnerabilities in produce safety. The FDA’s 2020 report pointed to possible contamination routes involving irrigation water, nearby cattle operations, and environmental pathways in the growing vicinity. It did not purport to close every gap, but it made clear that produce contamination is often an ecology problem as much as a plant-hygiene problem. Onions grow in the field. They are exposed to soil, water, dust, equipment, wildlife pressures, adjacent land uses, and harvest conditions that can all influence microbial safety. The lesson from 2020 was not merely that one farm or one lot had a problem; it was that field-level contamination routes in produce production can be subtle, difficult to prove conclusively after the fact, and devastating when they occur.
The fourth lesson is that international supply chains complicate outbreak resolution. The 2021 outbreak differed from 2020 in one critical respect: the implicated onions were imported from Chihuahua, Mexico. The peer-reviewed 2024 article on the 2021 Salmonella Oranienburg outbreak explains that traceback identified growers in Chihuahua capable of accounting for the exposures in the traceback investigation, but FDA was unable to conduct on-farm investigations in Mexico. The related Food Control publication abstract likewise notes that investigators could not determine a single source or route of contamination. That limitation is enormously important. It means that even when U.S. public-health investigators can identify the likely region and supply channels involved, practical barriers may prevent the kind of environmental root-cause work that could yield stronger preventive reforms.
That inability to do complete on-farm follow-up across borders is one of the most sobering lessons of the 2021 outbreak. A food-safety system is only as strong as its ability not only to detect and react, but to learn and correct. If regulators can identify the implicated onions but cannot fully examine the agricultural setting in which contamination likely occurred, then some of the most useful preventive insights remain out of reach. The 2021 outbreak therefore highlighted the importance of international cooperation, import oversight, recordkeeping, and stronger binational preventive systems for high-volume produce commodities.
A fifth lesson from both outbreaks is that whole-genome sequencing and coordinated public-health surveillance are indispensable. The CDC’s archived 2020 outbreak page and the bi-national peer-reviewed report on the 2020 outbreak show how genomic evidence helped connect U.S. and Canadian illnesses and link them to the same outbreak strain. Likewise, the CDC’s 2021 onion outbreak materials relied on epidemiologic and traceback data paired with the genetic fingerprinting infrastructure that now underpins modern outbreak work. Without those tools, these onion outbreaks might have looked like scattered sporadic cases in many places rather than coherent multistate epidemics. One lesson here is encouraging: outbreak detection has become far more powerful. But another is less comforting: the scale of those detected outbreaks suggests just how much contaminated product can move before the alarm is fully sounded.
A sixth lesson is that recalls alone are not enough if consumers cannot identify the implicated product. Onions present unique recall challenges. They are often sold loose, repacked, mixed with other ingredients, or stripped of detailed source labeling by the time they reach restaurants and home kitchens. In both 2020 and 2021, agencies issued cautious advice telling consumers not to eat onions if they could not determine the source. The CDC media release from August 2020 told consumers, restaurants, and retailers not to eat, serve, or sell onions from Thomson International, and if they did not know where their onions were from, not to eat or serve them. That kind of warning is necessary, but it also reveals a systemic weakness. When traceability becomes murky by the retail or food-service stage, outbreak control becomes more blunt and disruptive.
This leads to the seventh lesson: traceability for produce still needs improvement. The fact that onions from multiple varieties, multiple distributors, and multiple downstream products had to be swept into these recalls shows how quickly produce identification can become diluted once a commodity moves through commerce. Better lot-level traceability, better retention of source information in retail and food-service settings, and clearer consumer-facing information could help narrow public warnings and speed control measures. The onion outbreaks illustrate why traceability is not an abstract compliance issue. It is a core public-health tool.
An eighth lesson is that produce outbreaks often involve undercounting on a very large scale. The official outbreak numbers were already enormous. The 2020 outbreak involved more than 1,100 confirmed U.S. illnesses, and the 2021 outbreak exceeded 1,000 confirmed illnesses. But experienced outbreak investigators and public-health authorities have long recognized that confirmed cases usually represent only a fraction of actual illnesses. A Food Poisoning News article on the 2021 onion outbreak emphasized that the true number of victims was likely far higher than the official count. Although such extrapolations should be described cautiously, the underlying point is sound: many people never seek care, never submit stool samples, or are never linked to the outbreak. The lesson is that when an onion outbreak officially surpasses 1,000 cases, the real burden is almost certainly much larger.
The ninth lesson is that recurring outbreaks tied to the same general commodity should change risk perception. By the end of 2021, it was no longer plausible to think of onion-linked Salmonella outbreaks as freak events. The 2020 and 2021 outbreaks came after earlier onion-related outbreak experience as well, and the 2022 bi-national scientific report on the 2020 outbreak notes that from 2016 to 2019, dry bulb onions were the suspected cause of three multistate outbreaks in the United States. That is a striking observation. It suggests that by 2020, onions were already a commodity with a growing outbreak history. The lesson, then, is that recurring outbreaks should prompt more aggressive preventive attention rather than being treated as isolated surprises.
The tenth lesson is that environmental root-cause analysis must be faster and deeper. The FDA’s 2020 report was valuable because it attempted to identify possible contributing factors even without a conclusive answer. But the 2021 outbreak demonstrated how much is lost when that analysis cannot be fully performed at the source. If regulators and industry are serious about learning from these events, then the response cannot end with the recall. It must include environmental assessment, water-system evaluation, adjacent land-use analysis, sanitation review, harvesting and storage review, and cross-jurisdictional cooperation robust enough to support genuine prevention.
The eleventh lesson is that onions, like many fresh produce items, challenge the traditional consumer-safety message. Consumers are often told to wash produce and use good kitchen hygiene. Those steps matter, but they are not always enough for widely distributed contaminated produce. Onions are often chopped into salads, sandwiches, salsas, and garnishes or lightly cooked in ways that may not reliably eliminate pathogens. In restaurants and institutional settings, a single contaminated batch can be spread across a vast number of meals. The real lesson is that produce safety has to be built upstream. Once contaminated onions are in national commerce, the consumer is the last and weakest line of defense.
Finally, the onion outbreaks of 2020 and 2021 teach that “commodity familiarity” can be dangerous. Onions are ordinary. They are everywhere. They do not feel exotic or inherently risky. That very ordinariness may help explain why they can move so quietly through outbreak investigations before public understanding catches up. But from a food-safety standpoint, they deserve to be taken far more seriously than many consumers assume. The two outbreaks showed that onions can carry Salmonella across borders, across product categories, across kitchens, and across hundreds of hospitalizations.
In the end, the lesson of the 2020 and 2021 onion outbreaks is not simply that two bad years happened in a row. It is that the fresh-produce system received the same warning twice in rapid succession. The 2020 FDA investigation, the 2021 FDA investigation, the CDC’s final outbreak summaries for 2020 and 2021, and the post-outbreak scientific literature all point in the same direction. Produce contamination can be environmentally driven, traceability can be difficult, root-cause analysis can be incomplete, imported produce adds complexity, and onions are capable of causing very large, very widespread outbreaks. If there is a single overarching lesson, it is this: onions should no longer be treated as an unlikely Salmonella vehicle. The outbreaks of 2020 and 2021 settled that question. The real challenge now is whether regulators, growers, distributors, and food-service operators have learned enough from those outbreaks to prevent the next one.
