FoodNet 2021 Preliminary Data

Documenting the major sources of and trends in foodborne illness provides important information needed to determine whether prevention measures are working. Each year, FoodNet reports on the number of infections in the FoodNet surveillance area from pathogens transmitted commonly through food: Campylobacter, Cyclospora, Listeria, Salmonella, Shiga toxin-producing Escherichia coli (STEC), Shigella, Vibrio, and Yersinia. Laboratory tests, including cultures and culture-independent diagnostic tests (CIDTs), detected these pathogens.

Key Findings from 2021 Surveillance Data

Infections monitored by FoodNet decreased overall in 2021 compared with 2016–2018.

The COVID-19 pandemic likely played a role in the decrease.

Continued efforts are needed to prevent foodborne infections and meet national goals.

This year’s report summarizes 2021 preliminary surveillance data. It describes 2021 incidence compared with the average incidence for 2016–2018, the reference period used for the U.S. Department of Health and Human Services (HHS) Healthy People 2030 goals for some pathogens. The report also summarizes cases of hemolytic uremic syndrome (HUS) for 2020.

  • Observed incidences of enteric (intestinal) infections monitored by FoodNet decreased 8% overall in 2021 compared with the average during 2016–2018.
  • As in 2020, factors related to the COVID-19 pandemic likely influenced exposure to and detection of enteric infections.
    • Exposure: Interventions to slow the spread of COVID-19 and other changes in daily life likely decreased exposures to enteric pathogens.
    • Detection: Other factors, such as increased use of telemedicine and CIDTs, may have altered the detection of enteric infections.
  • Incidence of Salmonella infections decreased in 2021 compared with 2016–2018.
    • Salmonella was a large contributor to the overall decrease in infections.
    • Enteritidis, Newport, Typhimurium, Javiana, and I 4,[5],12:i:- have been the five most common Salmonella serotypes causing infection since 2010.
  • Incidence of Cyclospora, Vibrio, and Yersinia infections increased in 2021 compared with 2016–2018.
    • Increased use of CIDTs for these pathogens might have contributed to increased detection.
  • Incidence of Campylobacter, Listeria, Shigella, and STEC infections did not change in 2021 compared with 2016–2018.
  • Despite the overall decreases in infections during 2020 and 2021, continued efforts are needed to prevent foodborne infections and meet national goals, particularly for Campylobacter and Salmonella.
    • More comprehensive efforts might help reduce
      • Salmonella contamination of produce and poultry, and
      • Campylobacter contamination of chicken.
    • Vaccination of live chickens against certain Salmonella serotypes and improved hygiene during production could help decrease contamination of food.
  • Although CIDTs are fast and easy to use, reflex culturing following a positive CIDT is still needed to determine antibiotic resistance and make informed public health decisions.
  • During 2020, the incidence of HUS did not change. Although the incidence of STEC O157 (the most common cause of pediatric post-diarrheal HUS) decreased in 2020, the extent to which detections reflected actual decreases in illnesses is unknown.

Interpreting Changes in Incidence of Infections

How might the COVID-19 pandemic have affected infections tracked by FoodNet?

Interventions to limit the spread of COVID-19 likely decreased transmission of infections tracked by FoodNet in 2021, as it did in 2020. Though many regions lifted these interventions during portions of 2021, the overall incidence in infections tracked by FoodNet still decreased 8% compared with the pre-pandemic period of 2016–2018. Factors, such as broader use of telehealth, may have limited the diagnosis and detection of some cases. Because FoodNet captures laboratory-diagnosed infections, infections can be missed if ill people do not seek medical care and have a stool sample sent to a laboratory for testing.

Do we know everything that contributed to the observed trends?

No. Identifying all factors that contribute to observed incidences of infections is always challenging. The ever-changing nature of the COVID-19 pandemic and corresponding public health response during 2021 make this particularly challenging. Other unknown factors might have affected exposures, transmission, or detections.

Why did some pathogens decrease or increase more than others?

Assessing how various factors affected individual pathogens is difficult, and pathogens may have been subject to opposing forces. Some factors may have contributed to decreased transmission or detection and other factors may have contributed to increased transmission or detection.

Possible reasons for changes in transmission:

  • Decreases in international travel may have contributed to decreases in infections linked to travel.
  • Pandemic-related restaurant closures and changes in food preparation practices may have decreased transmission of foodborne infections.
  • Other pandemic control measures, such as school closures and social distancing, may have decreased transmission of some pathogens, particularly those transmitted commonly from person-to-person, such as Shigella.
  • Other factors, such as practices on farms or in slaughter or processing facilities, could have increased or decreased pathogen transmission via foods.

Possible reasons for changes in detection:

  • Changes in healthcare-seeking behaviors, such as increased use of telemedicine, may have resulted in fewer stool samples being tested by laboratories and some infections not being detected.
  • Increased use of CIDTs may have resulted in more infections being detected than would have been otherwise. These tests are sometimes better at detecting infections than stool cultures. However, reflex culture (growing the bacteria in a laboratory) is necessary to determine antibiotic resistance, detect outbreaks, and monitor concerning strains.
Why was 2016–2018 chosen as the reference period?

The reference period was chosen to match the reference period used for HHS’s Healthy People 2030 goals for Campylobacter, Listeria, Salmonella, and STEC. For recent reports, FoodNet has used the preceding three years as the reference period; for example, 2017–2019 was the reference period for 2020 data. However, previously FoodNet used a set three-year reference period (e.g., 1996–1998, 2006–2008) aligned with HHS’s Healthy People goals. Returning to this model, the 2016–2018 reference period will allow FoodNet to track progress toward achieving HHS’s Healthy People 2030 goals in the coming years. Furthermore, using this reference period avoids including 2020, which is not an ideal reference year given influences from the COVID-19 pandemic.

How does FoodNet estimate changes in the incidence of infection?

In 2022, FoodNet implemented a new model for estimating changes in the incidence of infection. The new Bayesian model is built on the previous frequentist model and adjusts for state-specific trends and changes in population over time. The model uses the average annual incidence for 2016–2018 for comparisons. Additional details can be found in the supplement, “An enhanced method for calculating trends in infections caused by pathogens transmitted commonly through food.”

Questions and Answers About Food Safety

Since 1996, FoodNet has been counting cases and tracking trends for infections transmitted commonly through food. Information gathered on which illnesses are decreasing and which are increasing provides a foundation for food safety policy and prevention efforts. FoodNet’s surveillance data, such as those in this report, show where efforts are needed to reduce foodborne illnesses. Learn more about FoodNet.

CDC uses the best scientific methods and information available to monitor, investigate, control, and prevent foodborne illness. Using epidemiology and laboratory science, CDC assesses public health threats. CDC works closely with state health departments to monitor the frequency of specific diseases and to conduct national surveillance for the diseases it monitors.

When food safety threats appear, CDC collaborates with public health partners, including state health departments, the U.S. Food and Drug Administration (FDA), and the U.S. Department of Agriculture (USDA), to conduct epidemiologic and laboratory investigations to determine the causes of these threats and how they can be controlled. Although CDC does not regulate the safety of food, CDC works with regulatory agencies to develop robust food safety policies and assess the effectiveness of current prevention efforts. CDC provides independent scientific assessment of what the problems are, how they can be controlled, and where the gaps exist in our knowledge. You can find more information on foodborne illness and CDC’s prevention activities on CDC’s Food Safety website.

Government regulation related to food safety is the responsibility of FDA, USDA’s Food Safety and Inspection Service (USDA-FSIS), the National Marine Fisheries Service, and other regulatory agencies.

Recent regulatory efforts include the following:

CDC works closely with regulatory agencies as they, along with industry, develop and implement measures to make our food safer.

Following four simple food safety steps – clean, separate, cook, and chill – can help protect you and your loved ones when preparing food at home.

Suggested citation: Centers for Disease Control and Prevention (CDC). Preliminary Incidence and Trends of Infections Caused by Pathogens Transmitted Commonly Through Food— Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2016–2021. MMWR Morb Mortal Wkly Rep. 2022 October 6.