Summer is peak season for many foodborne illnesses in the United States. Warmer temperatures, outdoor gatherings, and frequent handling of raw meat and fresh produce can create ideal conditions for bacteria and parasites to spread. From backyard cookouts to picnics and festivals, food safety risks rise significantly in the summer months.
This analysis draws on data from the National Notifiable Diseases Surveillance System (NNDSS), a nationwide program coordinated by the Centers for Disease Control and Prevention (CDC) to monitor the incidence of reportable diseases across all 50 states. The NNDSS collects laboratory-confirmed case counts from state and local health departments for a wide range of infectious diseases, including those caused by foodborne pathogens such as Salmonella, E. coli, and Listeria. These pathogens can cause a range of symptoms, including diarrhea, vomiting, abdominal cramps, and fever. While most cases are mild and resolve on their own, some infections can lead to serious complications such as kidney failure, bloodstream infections, or meningitis, particularly in young children, older adults, and people with weakened immune systems.
Using both recent national estimates and four years of finalized state-level data, researchers at Trace One—a product lifecycle management (PLM) and regulatory compliance software company for the food and beverage sector—examine three core questions: What are the most common foodborne pathogens tracked in the U.S.? How does the risk of foodborne illness vary throughout the year? And which states report the highest rates of illness? While the dataset does not capture every case—especially milder infections that go undiagnosed—it offers the most comprehensive look at geographic and seasonal trends in reported foodborne illness nationwide.
What Are the Most Common Foodborne Illnesses?
Campylobacter and Salmonella cause the greatest number of reported foodborne illnesses
Source: Trace One analysis of CDC NNDSS data
While many pathogens can cause foodborne illness, not all are included in national surveillance databases. The NNDSS tracks only a subset of foodborne diseases—those that are federally notifiable, laboratory-confirmable, and consistently reported by states. As a result, several of the most widespread causes of foodborne illness in the U.S., including norovirus, Clostridium perfringens, and Bacillus cereus, are not captured by the NNDSS. These pathogens often lead to short-lived illnesses and are rarely lab-confirmed.
The analysis presented here focuses on the eight most common pathogens tracked by NNDSS that are associated with foodborne transmission and common causes of food recalls: Campylobacter, Salmonella, Shigella, Shiga toxin-producing E. coli (STEC), Cryptosporidium, Cyclospora, Vibrio, and Listeria. Among these, Campylobacter and Salmonella are by far the most frequently reported. In 2024, the national case rate for Campylobacter reached 23.4 cases per 100,000 people, up from 22.1 the previous year. Salmonella followed with 17.9 cases per 100,000, also increasing from 16.0 in 2023. These pathogens are commonly linked to contaminated retail meats, eggs, unpasteurized dairy, and fresh produce.
Other tracked pathogens cause illnesses at lower rates but still pose significant risks, especially for vulnerable populations. In 2024, Shigella was reported at 6.0 cases per 100,000, followed by STEC (4.7), Cryptosporidium (3.5), Cyclospora (1.1), Vibrio (1.0), and Listeria (0.2). Though rarer, infections linked to Listeria and Vibrio are often more severe and can result in hospitalization or death, particularly among vulnerable populations.
What Time of Year Are Foodborne Illnesses Most Common?
Over 33% of foodborne illness cases occur between June and August
Source: Trace One analysis of CDC NNDSS data
Foodborne illnesses in the United States show a distinct seasonal pattern, with reported cases peaking in the summer. According to the preliminary 2024 data from the CDC, nearly one-third (33.1%) of all foodborne illness cases occurred between June and August. This seasonal spike reflects a combination of environmental and behavioral factors: warmer temperatures that promote bacterial growth, increased outdoor food preparation, and a greater consumption of fresh (uncooked) produce.
Among summer months, August had the highest share of reported cases at 12.4%, followed by June (11.3%) and July (9.4%). In contrast, winter months such as January and February saw much lower case counts, accounting for just 5.0% and 5.6% of the annual total, respectively. However, not all foodborne pathogens follow this summer pattern. Norovirus, for example—though not included in this analysis—is known to peak during the winter months, largely due to its high contagiousness and the increased amount of time people spend indoors.
Some pathogens display especially concentrated seasonal patterns. Cyclospora, a parasite linked to fresh produce, shows a sharp summer peak with nearly half of all Cyclospora cases on record reported in July alone. These trends underscore the need for timely public health messaging and extra attention to food safety, especially during times of higher risk.
Rates of Foodborne Illness by State
Neighboring SD, NE, MN, and WY have the highest rates of reported illnesses
Source: Trace One analysis of CDC NNDSS data
Rates of reported foodborne illness vary significantly across states, with certain regions—particularly in the Northern Plains and Upper Midwest—reporting notably higher incidence. According to aggregated data from the most recent four years of finalized NNDSS records, South Dakota reported the highest overall rate at 92.2 cases per 100,000 people, more than double the national average of 48.8. Nebraska (74.4), Minnesota (66.6), and Wyoming (66.4) closely followed, forming a contiguous cluster of high-reporting states in the central U.S.
This geographic pattern suggests both regional exposure risks and potentially higher rates of diagnostic testing and case reporting in these areas. In contrast, several other high-ranking states are geographically and demographically diverse. Vermont (62.0), Florida (61.9), and Wisconsin (60.5) also reported elevated rates, as did parts of the Mountain West such as Montana (59.7) and New Mexico (58.8). Larger states like New York (58.3) and California (48.9) fell near the national average but still ranked among the top half of states.
Lower rates were observed in parts of the Midwest and Northeast, including Michigan (33.3), Indiana (33.7), and Maine (33.6), while Alaska reported the lowest rate in the nation at 27.0 per 100,000. While variations in food supply chains and dietary habits may contribute to these patterns, differences in public health infrastructure, surveillance practices, and how likely individuals are to seek healthcare also influence state-level rates. As such, these figures likely reflect a combination of true differences in disease burden and variability in reporting practices.
For additional information and complete results for all states, see States With the Highest Rates of Foodborne Illnesses on Trace One.
Methodology
Photo Credit: Cast Of Thousands / Shutterstock
This analysis examines the states with the highest reported rates of foodborne illnesses in the United States, based on data from the National Notifiable Diseases Surveillance System (NNDSS) maintained by the Centers for Disease Control and Prevention (CDC). National-level statistics are from the CDC’s 2024 preliminary weekly estimates, while state-level statistics represent the most recent four years of finalized records (2019–2022), accessible through the CDC’s WONDER database.
The analysis focuses on eight foodborne pathogens for which surveillance data are most consistently available. These pathogens include Campylobacter, Salmonella, Shigella, Shiga toxin-producing Escherichia coli (STEC), Cryptosporidium, Cyclospora, Vibrio, and Listeria. Notably, norovirus—a leading cause of foodborne illness—is excluded from this analysis because it is not a reportable disease and cases are often mild and undiagnosed.
Incidence rates were calculated as the number of reported cases per 100,000 population. For each state, the most disproportionately represented pathogen was determined by calculating the percentage by which the state-specific rate for each exceeded the national rate. The pathogen with the highest percentage difference was flagged as the most overrepresented in that state. Only states that reported data for all eight tracked pathogens were included in the final results.
It is important to acknowledge the limitations of the NNDSS dataset. Reporting practices vary by state due to differences in public health infrastructure, diagnostic testing capacity, and case follow-up procedures. As a result, geographic differences in incidence rates may reflect not only actual differences in disease burden, but also variations in detection and reporting. Moreover, many mild cases of foodborne illness go unreported, leading to an underestimation of true incidence. Despite this, NNDSS provides the most comprehensive and standardized data available for tracking reportable foodborne diseases in the U.S.
For complete results, see States With the Highest Rates of Foodborne Illnesses on Trace One.
