Preliminary Incidence and Trends of Infections Caused by Pathogens Transmitted Commonly Through Food

Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2022

Miranda J. Delahoy, PhD; Hazel J. Shah, MPH; Daniel Lowell Weller, PhD; Logan C. Ray, MPH; Kirk Smith, DVM, PhD; Suzanne McGuire, MPH; Rosalie T. Trevejo, DVM, PhD; Elaine Scallan Walter, PhD; Katie Wymore, MPH; Tamara Rissman, MPH; Marcy McMillian, MPH; Sarah Lathrop, DVM, PhD; Bethany LaClair, MPH; Michelle M. Boyle, MPH; Stic Harris, DVM; Joanna Zablotsky-Kufel, PhD; Kennedy Houck, MPH; Carey J. Devine, MPH; Carey E. Lau; Robert V. Tauxe, MD; Beau B. Bruce, MD, PhD; Patricia M. Griffin, MD; Daniel C. Payne, PhD


Morbidity and Mortality Weekly Report. 2023;72(26):701-706. 

In This Article

Abstract and Introduction


Each year, infections from major foodborne pathogens are responsible for an estimated 9.4 million illnesses, 56,000 hospitalizations, and 1,350 deaths in the United States.[1] To evaluate progress toward prevention of enteric infections in the United States, the Foodborne Diseases Active Surveillance Network (FoodNet) conducts surveillance for laboratory-diagnosed infections caused by eight pathogens transmitted commonly through food at 10 U.S. sites. During 2020–2021, FoodNet detected decreases in many infections that were due to behavioral modifications, public health interventions, and changes in health care–seeking and testing practices during the COVID-19 pandemic. This report presents preliminary estimates of pathogen-specific annual incidences during 2022, compared with average annual incidences during 2016–2018, the reference period for the U.S. Department of Health and Human Services' Healthy People 2030 targets.[2] Many pandemic interventions ended by 2022, resulting in a resumption of outbreaks, international travel, and other factors leading to enteric infections. During 2022, annual incidences of illnesses caused by the pathogens Campylobacter, Salmonella, Shigella, and Listeria were similar to average annual incidences during 2016–2018; however, incidences of Shiga toxin-producing Escherichia coli (STEC), Yersinia, Vibrio, and Cyclospora illnesses were higher. Increasing culture-independent diagnostic test (CIDT) usage likely contributed to increased detection by identifying infections that would have remained undetected before widespread CIDT usage. Reducing pathogen contamination during poultry slaughter and processing of leafy greens requires collaboration among food growers and processors, retail stores, restaurants, and regulators.

CDC, 10 state health departments, the U.S. Department of Agriculture's Food Safety and Inspection Service (FSIS), and the Food and Drug Administration (FDA) collaborate to conduct active population-based surveillance of the FoodNet catchment area,* which included an estimated 51 million persons in 2022 (approximately 15% of the U.S. population). Laboratories diagnose bacterial infections by culture or CIDT and Cyclospora infections by microscopy or polymerase chain reaction. Infection incidence was calculated by dividing the number of infections during 2022 by 2021 U.S. Census Bureau population estimates for the surveillance area and is reported as infections per 100,000 persons. A Bayesian, negative binomial model with penalized thin plate splines adjusting for state-specific trends and population changes§ was used to estimate incidence changes during 2022 compared with the average annual incidence during 2016–2018 using the brms package (version 2.14.0) in R software (version 3.6.2, R Foundation). Incidence was described as increased or decreased relative to the reference period if the 95% credible interval (CrI) for the incidence rate ratio (IRR) did not cross the null value of 1. Incidence changes were also estimated using this method for the subset of infections that were domestically acquired.** Frequencies of hospitalizations, deaths, outbreak-associated infections, and international travel-associated infections were calculated overall and by pathogen.†† The proportion of infections that were diagnosed by CIDT§§ and diagnosed only by CIDT (meaning the specimen had a negative culture result or was not cultured), the proportion of infections diagnosed by CIDT for which a culture was performed, and the proportion of those cultures yielding an isolate were calculated by pathogen for bacterial infections.

A network of nephrologists and infection preventionists conducts surveillance for diagnosed pediatric post-diarrheal hemolytic uremic syndrome (HUS), a complication of STEC infection that most commonly occurs among young children; additional HUS data are collected by hospital discharge review.¶¶ This report includes HUS cases and incidence per 100,000 children and adolescents aged <18 years detected during 2021, the most recent year with available data. This activity was reviewed by CDC and conducted consistent with applicable federal law and CDC policy.***

During 2022, FoodNet identified 25,479 cases of infection, 5,981 hospitalizations, and 170 deaths (Table 1). Infection incidence was highest for Campylobacter (19.2 cases per 100,000 population), followed by Salmonella (16.3). Compared with pathogen-specific average annual incidences during 2016–2018, STEC, Yersinia, Vibrio, and Cyclospora infection incidences were higher during 2022. Overall infection incidence was stable for Campylobacter, Salmonella, Shigella, and Listeria. However, when limited to domestically acquired infections, Campylobacter incidence was higher during 2022 (IRR = 1.07, 95% CrI = 1.01–1.14), as were incidences for Yersinia, Vibrio, and Cyclospora. Compared with 2016–2018, similar percentages of infections during 2022 resulted in hospitalization (23.5% in 2022 versus 23.8%) and death (0.7% versus 0.5%) or were associated with outbreaks (4.3% versus 3.9%) or international travel (12.4% versus 12.8%). However, 62 Salmonella infections (0.7%) resulted in death during 2022, compared with an annual average of 37 (0.4%) during 2016–2018. Serotypes and characteristics of Salmonella infections resulting in death were similar to those during 2016–2018 (FoodNet, unpublished data, 2023).†††

Among 7,032 Salmonella infections with positive culture results during 2022, 6,345 isolates (90%) were fully serotyped. The five most common serotypes were Enteritidis (2.7 cases per 100,000 population), Typhimurium (1.6), Newport (1.4), Javiana (0.9), and I 4,[5,12:i:- (0.6), which have been the five most common serotypes each year since 2010. The incidences of two of these serotypes were lower during 2022 compared with those during 2016–2018: Enteritidis (IRR = 0.88, 95% CrI = 0.79–0.97) and I 4,[5],12:i:- (IRR = 0.69, 95% CrI = 0.56–0.86).

Among 2,882 STEC infections, specimens for 2,401 (83%) were cultured; 1,298 (54%) of those cultured yielded an isolate. The O antigen was determined for 1,187 (91%) of the cultured isolates; among those, serogroup O157 was most common (301; 25%), followed by O103 (164; 14%), O26 (155; 13%), and O111 (149; 13%). During 2021, 72 cases of post-diarrheal HUS among persons aged <18 years were reported (0.7 cases per 100,000) (IRR relative to 2016–2018 = 0.96, 95% CrI = 0.82–1.13), including 41 (57%) among persons <5 years old (1.5 per 100,000) (IRR = 0.95, 95% CrI = 0.79–1.18).

The percentage of bacterial infections diagnosed using CIDT increased from 49% during 2016–2018 to 73% in 2022 (Table 2). The percentage of bacterial infections diagnosed using only CIDT increased from 26% during 2016–2018 to 41% in 2022, and, by pathogen, was highest for Yersinia (77%), Vibrio (56%), and STEC (55%). The overall proportion of reflex cultures that yielded an isolate was similar during 2016–2018 (65%) and 2022 (62%), but decreased for Salmonella, STEC, Shigella, Vibrio, and most markedly for Yersinia (from 48% to 24%).

*The FoodNet catchment includes Connecticut, Georgia, Maryland, Minnesota, New Mexico, Oregon, Tennessee, and selected counties in California, Colorado, and New York.
Reflex culture refers to the process of attempting to grow the identified pathogen in a laboratory culture medium after a CIDT-positive result. Reflex culture practices vary by state and pathogen, and depend on resources, state isolate submission requirements, and specimen viability.
Incidence for each year is calculated by dividing the number of infections during that year by the previous year's U.S. Census Bureau population estimate for the surveillance area. The average during 2016–2018 was calculated by averaging the three incidences for the years 2016, 2017, and 2018.
**Domestically acquired infections are defined as those for which the patient had no history of international travel or unknown travel history. A history of international travel refers to reported international travel during the 30 days before illness began for Listeria and Salmonella serotypes Typhi and Paratyphi, 14 days before illness began for Cyclospora, and 7 days before illness began for other pathogens. Travel information was missing for 24% of infections.
††Responses that were unknown were included in proportion denominators.
§§Refers to infections for which the specimen had a culture performed, regardless of the result, and infections for which the specimen was not cultured.
¶¶To augment HUS case findings by pediatric nephrologists and infection control practitioners, FoodNet staff members annually review hospital discharge data for pediatric HUS cases to validate surveillance reports and identify additional cases by using International Classification of Diseases, Tenth Revision (ICD-10) and ICD-11 codes specifying HUS, acute renal failure with hemolytic anemia and thrombocytopenia, or thrombotic thrombocytopenic purpura with diarrhea caused by an unknown pathogen or E. coli.
***45 C.F.R. part 46.102(l)(2), 21 C.F.R. part 56; 42 U.S.C. Sect. 241(d); 5 U.S.C. Sect. 552a; 44 U.S.C. Sect. 3501 et seq.
†††The most common serotypes associated with Salmonella deaths both during 2022 and during 2016–2018 were Enteritidis and Typhimurium. The median age for patients with Salmonella deaths during 2022 was 67 years (IQR = 56–76 years) and during 2016–2018 was 68 years (IQR = 53–78 years). During 2022, 10% of Salmonella deaths were associated with outbreaks compared with 5% during 2016–2018. In addition, during 2022, 3% of the Salmonella deaths with reported travel history were associated with international travel compared with 2% during 2016–2018. The numbers are small, limiting ability to detect differences between reporting periods.