TL;DR: One in ten FDA-reviewed foodborne illness incidents from 2011 to 2025 was caused by a chemical hazard, not a microbe, with seafood toxins leading the list.
A new review published on 26 May 2026 in Frontiers in Toxicology reports that the Coordinated Outbreak Response and Evaluation (CORE) Network evaluated 1,270 foodborne illness incidents from 2011 to 2025 and attributed 127 incidents, or 10%, to a chemical exposure. The authors are Brett Weed, Lauren Yeung, Omari Bandele and Cary Chen Parker of the Human Foods Program at the U.S. Food and Drug Administration in College Park, Maryland. Seafood toxins from shellfish and finfish represented the majority of these chemical incidents, followed by illicit or pharmaceutical drugs, toxic elements and botanical toxins.
The paper presents several case studies that represent an array of classes of chemical hazards and distinct root causes of contamination. Its central message for consumers, clinicians and food operators is that chemical incidents are less common than microbial outbreaks but present additional complexities. Those complexities include a lack of established surveillance and reporting systems for chemical incidents, difficulties in demonstrating a connection between illness presentation and a specific exposure to a given food product, and the heterogeneity of contamination. The authors also report that many outbreaks require development and validation of new analytical methods for a novel food-contaminant pair to generate laboratory results sufficient to support regulatory action.
What the 1,270-incident review counted
The analysis was extracted from the CORE database of foodborne illness incidents, according to Frontiers in Toxicology. The database includes detailed information on foodborne outbreaks that were evaluated and investigated by FDA from the creation of CORE in 2011 to the present. The authors state that the data do not represent all outbreaks associated with FDA-regulated human foods, and that the data represent outbreaks with FDA involvement.
Within that FDA-involved set, CORE evaluated 1,270 foodborne illness incidents between 2011 and 2025. Of those, 127 incidents were attributable to a chemical exposure. The share was 10%. That framing is important for interpretation. The figure describes the proportion of chemical causes within incidents that reached FDA’s CORE process, not an estimate of the share of all foodborne illnesses in the United States caused by chemicals.
The authors distinguish terminology used throughout the review. In the manuscript, “chemical hazard” refers to the causative chemical agent or contaminant, whereas “chemical incident” refers to a foodborne illness event or outbreak investigation attributed to such a hazard. A chemical hazard is therefore the substance, while a chemical incident is the illness event investigated.
The ranking of hazard groups is also explicit. Seafood toxins, from both shellfish and finfish, represented the majority of the 127 chemical incidents. Illicit or pharmaceutical drugs were next, followed by toxic elements and botanical toxins. The review states that several case studies are presented which represent an array of classes of chemical hazards and distinct root causes of contamination.
Why chemical outbreaks are harder to detect
Investigations of foodborne exposure to chemical substances are complex and often a causative agent cannot be definitively identified, the review notes. While extensive research has been dedicated to estimating the burden attributable to microbial pathogens, estimates of the total burden of illness due to chemical hazards are not well-defined.
The paper places that gap in context by citing a global estimate for metals. Foodborne illnesses from just four toxic metals, arsenic, cadmium, lead and methylmercury, were estimated at one million cases and 56,000 deaths globally in 2015. Foodborne illness itself can be caused by biological, chemical or physical hazards.
Lead author Brett Weed summarized the practical difference in a companion post on 26 May 2026. He wrote that the team examined almost 1,300 outbreaks evaluated by CORE from its founding in 2011 to 2025 and identified 127, or 10%, caused by a chemical hazard rather than a pathogen. He added that seafood toxins predominate, but outbreaks were also caused by a wide variety of other chemicals and toxins.
Weed also listed three investigation barriers. Chemical outbreaks have no genomic fingerprint to show relatedness in surveillance systems, signs and symptoms may present differently in different patients, and laboratory assays may not exist for the food-chemical pair implicated. He wrote that awareness of the uniqueness of chemical outbreak investigations may speed the identification and mitigation of these outbreaks when they occur.
The peer-reviewed paper makes the same points in formal terms. The stated challenges include a lack of established surveillance and reporting systems for chemical incidents. They also include difficulties in demonstrating a connection between illness presentation and a specific exposure to a given food product. A third stated challenge is the heterogeneity of contamination. A fourth is the need, in many outbreaks, for development and validation of new analytical methods for a novel food-contaminant pair to generate laboratory results sufficient to support regulatory action.
How FDA, CDC and states investigate an outbreak
Foodborne illness outbreak investigations involve coordinated efforts among federal, state and local public health and regulatory agencies to identify outbreak sources and prevent additional illnesses, according to Frontiers in Toxicology. Investigators collect and analyze three types of data to determine the common food consumed by ill people.
First, epidemiologic data are gathered as state and local partners work with the Centers for Disease Control and Prevention to identify outbreaks and common foods consumed by ill individuals through public health surveillance. Second, traceback data are collected when state and local authorities collaborate with FDA to examine the food supply chain and determine the origin of suspected foods identified from epidemiologic evidence. Third, laboratory data are obtained through product and environmental sampling.
These three types of data are evaluated holistically to confirm the contaminated food, with confirmation requiring support from at least two of the three categories. While outbreaks due to microbial hazards are supported by well-established surveillance systems and laboratory protocols, chemical incidents often rely on less formal or syndromic surveillance and often present obstacles to rapid laboratory identification of chemical hazards.
CORE serves as FDA’s coordination focal point for outbreak investigations in foods and dietary supplements. CORE comprises eight specialized teams, each with distinct responsibilities in the outbreak response process. These teams evaluate emerging outbreaks and disease surveillance trends in collaboration with CDC, FDA field offices and state and local agencies. They coordinate investigations, inspections, sampling and product distribution tracing to control and stop outbreaks.
The teams also monitor investigations and issue public warnings when there is ongoing risk with actionable steps to reduce illness. Following outbreak responses, CORE conducts analyses to recommend preventative measures for food safety activities. The paper states that FDA is committed to detecting, mitigating and preventing chemical hazards in foods, including targeted public health surveillance programs, laboratory method development, and partnerships with other public health and food safety agencies to ensure a safe food supply for U.S. consumers.
What national surveillance captures — and misses
Context on routine outbreak surveillance comes from the CDC system described in CDC Foodborne Outbreak Data: The Federal Database Behind Every US Food Poisoning Investigation. That explainer reports that the Foodborne Disease Outbreak Surveillance System is operated by the CDC Division of Foodborne, Waterborne, and Environmental Diseases. State and local health departments investigate foodborne illness outbreaks and submit outbreak reports to CDC, and the system aggregates these reports into the national database.
An outbreak is defined as two or more persons experiencing a similar illness after consuming food or beverages from a common source. Single sporadic cases are not counted. That definition sets an immediate limit on what the system captures, because a person who never seeks care, or whose illness is never linked to a cluster, contributes no record to the system.
Records are submitted through the National Outbreak Reporting System, a web-based platform that replaced paper reporting forms beginning in 2009. The system collects structured data on each outbreak, including pathogen with confirmed or suspected status, food vehicle, food preparation setting, contamination factor, number of ill persons, hospitalizations, deaths and laboratory confirmation status. Cases with confirmed etiology, where laboratory testing identified the causative pathogen, are distinguished from those with suspected etiology based on incubation period, symptoms and epidemiological pattern.
The explainer reports that approximately 800 to 1,000 outbreaks are reported each year, generating roughly 15,000 illnesses, 800 hospitalizations and 20 deaths among reported outbreak cases. Annual results are published in the Morbidity and Mortality Weekly Report as “Surveillance for Foodborne Disease Outbreaks, United States.” The same source reports CDC estimates that 48 million Americans experience foodborne illness each year from all causes, resulting in 128,000 hospitalizations and 3,000 deaths annually. That contrast shows that reported outbreaks capture a small visible portion of a larger burden, reflecting underreporting at each step from care-seeking to investigation.
The review’s point about surveillance fits that structure. Microbial outbreaks are supported by established laboratory protocols and genomic relatedness tools, while chemical incidents often depend on syndromic signals and custom laboratory work. When no validated assay exists for the implicated food-chemical combination, investigators must first build and validate a method before results can support regulatory action.
What this means for seafood, drugs, metals and plant toxins
For readers planning meals, the most direct finding is the ranking. Seafood toxins from shellfish and finfish were the majority cause among the 127 chemical incidents with FDA involvement. Illicit or pharmaceutical drugs were the next group named, followed by toxic elements and botanical toxins. The paper uses case studies to show distinct root causes across hazard classes, rather than a single failure point.
The toxic-metals context underscores why prevention matters beyond acute outbreaks. The cited global estimate for 2015 attributes one million cases and 56,000 deaths to foodborne illnesses from arsenic, cadmium, lead and methylmercury. That figure is a global burden estimate for four metals, not a U.S. outbreak count, and the authors cite it to show that chemical exposures can carry large health consequences even when outbreak counts look small.
The operational lesson is about reporting and testing. Because chemical illness can vary between patients, and because contamination can be heterogeneous within a product or lot, linking cases to one food requires epidemiologic, traceback and laboratory evidence together. Confirmation needs support from at least two of those three evidence categories. When clinicians, patients and food businesses preserve product, packaging and purchase records and report promptly to state or local health departments, the epidemiologic and traceback legs of that process have more material to work with.
The regulatory lesson is about methods and partnerships. The authors state that FDA’s work includes targeted public health surveillance programs, laboratory method development, and partnerships with other public health and food safety agencies. Those three activities correspond directly to the three barriers named: surveillance and reporting systems for chemical incidents, analytical methods for novel food-contaminant pairs, and coordinated action with CDC, FDA field offices and state and local agencies.