CDC study identifies leading culprits of foodborne illness

By Dr. Sanchari Sinha Dutta, Ph.D.Mar 25 2025

Using advanced diagnostics and improved modeling, the CDC reveals which foodborne bugs are making Americans sick—and how many end up in hospital beds or worse.

Study: Foodborne Illness Acquired in the United States—Major Pathogens, 2019. Image Credit: Corona Borealis Studio / Shutterstock

The US Centers for Disease Control and Prevention (CDC), in association with the Colorado School of Public Health, USA, reported recent estimates of the numbers of illnesses, hospitalizations, and deaths caused by seven foodborne pathogens in the United States in 2019. A detailed report has been published in the CDC’s journal, Emerging Infectious Diseases.

Background

In the United States, laboratory-confirmed illnesses caused by foodborne pathogens are routinely reported to public health departments, providing valuable information to help allocate resources and prioritize interventions. However, underreporting and underdiagnosis are two significant challenges faced by public health surveillance systems, as not all patients seek medical assistance or receive a diagnosis, making it difficult to provide accurate estimates. The CDC periodically estimates the number of foodborne illnesses by adjusting for undercounts in surveillance data to overcome reporting challenges. Since the last report was published in 2011, new data and diagnostic methods have emerged, and new regulations and interventions have been implemented to prevent foodborne illnesses.

In this recent report, researchers focused on seven foodborne pathogens, including Campylobacter spp., Clostridium perfringens, invasive Listeria monocytogenes, norovirus, nontyphoidal Salmonella serotypes, Shiga toxin–producing Escherichia coli (STEC), and Toxoplasma gondii, which are considered to be the leading causes of domestically acquired foodborne illnesses, hospitalizations, and deaths in the United States.

Study Findings

The study estimates revealed that the included pathogens caused approximately 9.9 million domestically acquired foodborne illnesses in 2019. These illnesses were associated with an estimated 53,300 hospitalizations and 931 deaths.

Among the selected pathogens, norovirus was responsible for the majority of domestically acquired foodborne illnesses, followed by Campylobacter spp., nontyphoidal Salmonella, C. perfringens, STEC, and invasive L. monocytogenes. T. gondii was not included in the illness estimates because most infections are asymptomatic. Norovirus was also the leading cause of hospitalizations (22,400 hospitalizations per year) associated with domestically acquired foodborne illnesses, followed by Campylobacter spp., nontyphoidal Salmonella, STEC, invasive L. monocytogenes, T. gondii, and C. perfringens.

Nontyphoidal Salmonella was responsible for most of the deaths (238 deaths per year) associated with domestically acquired foodborne illnesses, followed by Campylobacter spp., norovirus, invasive L. monocytogenes, STEC, T. gondii, and C. perfringens.

Among selected pathogens, invasive L. monocytogenes caused 1,050 non–pregnancy-associated and 198 pregnancy-associated illnesses; 920 non–pregnancy-associated and 148 pregnancy-associated hospitalizations; and 166 non–pregnancy-associated and 6 pregnancy-associated deaths, all among infants.

Study Significance

The study finds that foods contaminated with Campylobacter spp., C. perfringens, invasive L. monocytogenes, nontyphoidal Salmonella, STEC, and norovirus caused approximately 9.9 million domestically acquired foodborne illnesses in the United States in 2019. Toxoplasma gondii was assessed only for hospitalizations and deaths due to lack of data on symptomatic illness. These six pathogens, along with Toxoplasma gondii, resulted in approximately 53,300 hospitalizations and 931 deaths in the same year.

These 2019 estimates are higher than the estimates published in 2011. This may be due to the discovery of culture-independent diagnostic tests (CIDTs), which were introduced to the market in 2013 and adopted by most clinical laboratories as a superior alternative to culture-based methods. These methods are capable of identifying more pathogens that might have otherwise gone undetected and unreported in US surveillance systems. CIDTs were especially valuable in improving detection of pathogens like non-O157 STEC, which were previously harder to identify.

The advanced strategies adopted in the current study to adjust for underdiagnosis also contribute to higher estimates of illnesses caused by Campylobacter spp., nontyphoidal Salmonella, and STEC. Compared to previous estimates, the underdiagnosis multipliers for these pathogens were increased, reflecting a broader range of contributing factors beyond just bloody diarrhea. Besides adjusting for bloody diarrhea, the study included additional factors, such as illness duration, recent foreign travel, age, and socioeconomic status, in the current estimates as potential drivers of medical care-seeking behaviors. These factors might have contributed to the increased magnitude of underdiagnosis multipliers for these pathogens.

Limitations

Estimates of the percentage of food-transmitted illnesses and travel-related illnesses can significantly affect the results and have important limitations. Due to the scarcity of data for estimating foodborne illness percentages, the study utilized data from a structured expert judgment. One potential limitation of this approach is the risk of expert bias. However, this approach provided consistency across all pathogens and ensured that transmission through all possible modes added up to 100%.

The study used surveillance data to estimate the percentage of travel-related illnesses for most pathogens. However, it has recently been reported that international travel is associated with medical care-seeking behaviors, indicating a possibility of overestimating travel-related illnesses in this report.

The study included data from various sources, which had varying quality and representativeness. For example, C. perfringens data were derived from outbreak-associated cases, which may not reflect all illnesses. While data related to Campylobacter spp., nontyphoidal Salmonella, and STEC were obtained from an active surveillance system representing a 15% convenience sample of the US population, estimates of norovirus and T. gondii were based on administrative data sources that are not nationally representative.

Moreover, illnesses caused by certain pathogens, including T. gondii (for which mild illnesses were not estimated) and L. monocytogenes, may be underrepresented. Although the study estimated the number of fetal deaths caused by L. monocytogenes, there is a possibility that early spontaneous abortion or miscarriage remained underdiagnosed. The study also notes that lower estimates of T. gondii-related hospitalizations and deaths compared to previous reports may reflect improved HIV treatment, which reduces reactivation risk.