An Update on Foodborne Illness

Column Author and Editor: Chris Day, MD | Pediatric Infectious Diseases; Director, Transplant Infectious Disease Services; Medical Director, Travel Medicine; Assistant Professor of Pediatrics, University of Missouri-Kansas City School of Medicine; Clinical Assistant Professor of Pediatrics, University of Kansas School of Medicine

As I write this column, in mid-July, we are at the typical peak season for outbreaks of foodborne illnesses due to Salmonella, Campylobacter, Listeria and Shiga toxin-producing E. coli (STEC).¹ Not coincidentally, this is also a time of year when more people are cooking and eating outdoors, which can be associated with less safe food safety practices. Warm weather contributes to more rapid growth of bacteria, whether on green leafy vegetables, in poultry farms or at other points in the food supply chain.  

Foodborne illnesses are a major health problem. Using data from the Foodborne Diseases Active Surveillance Network (FoodNet), the Centers for Disease Control and Prevention (CDC) has periodically estimated the total impact of foodborne illness in the U.S. In the most recent such estimate from 2011, the CDC documented 9.4 million annual episodes of foodborne illness (90% credible interval [CrI] 6.6-12.7 million) caused by 31 known (“major”) pathogens. The CDC further estimates that 55,961 annual hospitalizations (90% CrI 39,534-75,741) (caused most often by Salmonella, norovirus or Campylobacter) and 1,351 deaths (most often due to Salmonella, Toxoplasma gondii, Listeria monocytogenes or norovirus) are caused by these pathogens.² Estimates for foodborne gastroenteritis caused by “unspecified agents” are even higher (38.4 million episodes of illness annually (90% CrI 19.8-61.2 million).³ 

Salmonella, Campylobacter, Listeria, STEC, Shigella, Yersinia, Vibrio and Cyclospora are under surveillance through FoodNet, a collaboration of the CDC, state health departments, the U.S. Department of Agriculture’s Food Safety and Inspection Service (FSIS), and the Food and Drug Administration (FDA) conducted at 10 sites in the United States. While FoodNet-detected incidence of infections with these pathogens declined during 2020-2021 (thought to be due to COVID-19 pandemic-related measures and changes in patient and provider behaviors, including health care-seeking and testing practices), annual incidence of these illnesses in 2022 either returned to the prior baseline (Campylobacter, Salmonella, Shigella and Listeria) or increased (STEC, Yersinia, Vibrio and Cyclospora) compared to 2016-2018. The CDC notes a lack of progress in reducing incidence of these infections. FSIS published new guidelines in 2021 to reduce pathogen colonization in poultry through vaccination, prebiotics, probiotics, and minimizing contamination of poultry water, feed, and bedding and has proposed new regulations to control Salmonella in poultry products. The FDA is working on rules to improve agricultural water safety to reduce contamination of leafy greens, particularly to prevent STEC.⁴ 

Laboratory methods used for detecting foodborne pathogens are changing over time with use of culture-independent diagnostic tests (CIDTs), particularly nucleic acid amplification tests (NAATs). Approximately one-half of bacterial foodborne infections were detected by CIDT in 2016-2018; by 2021, two-thirds of infections were detected by such methods.⁴ There are potentially some clinical and public health advantages to CIDTs, including detection of pathogens for which tests were not previously available (e.g., norovirus) and increased detection of some other pathogens. However, such tests generally do not distinguish between different bacterial strains and subtypes and do not provide information on bacterial susceptibilities. Among other problems, clinical interpretations of these tests are not always straightforward due to detection of organisms of unclear significance. Pathogen identification by CIDT alone can also make outbreak detection more difficult with potentially significant public health consequences. CDC is encouraging test manufacturers and clinical laboratories to find ways to continue to culture pathogens found in stool in the setting of positive CIDTs. Long term, more advanced CIDTs may provide information about strain, subtype, pathogenicity and antibiotic resistance without the need for cultures,⁵ overcoming the current difficulties. 

Although substantial progress in reducing the incidence of foodborne infections will likely be driven by government policies and technologic progress, consumers can currently protect themselves by following food safety recommendations. Adherence to recommendations is particularly important for members of groups at high risk for more serious consequences from infection, including people with weakened immune systems, older adults and children under 5 years old. Children under 5 are three times more likely to be hospitalized if they get a Salmonella infection⁶ and are at much higher risk of any age group for having hemolytic uremic syndrome (HUS) with E. coli O157 infections.⁷ The CDC and the Department of Health and Human Services (in partnership with the U.S. Department of Agriculture, the CDC and the FDA) both separately maintain webpages that provide tips on food safety.^8,9 The foodsafety.gov site includes several helpful tables including guides on cold food storage, food safety during a power outage, safe minimum internal temperatures, and meat and poultry roasting and thawing. Safe eating to you all and all of your patients. 

References: 

1. Simpson RB, Zhou B, Naumova EN. Seasonal synchronization of foodborne outbreaks in the United States, 1996–2017. Sci Rep. 2020;10(1):17500. doi:10.1038/s41598-020-74435-9  
2. Scallan E, Hoekstra RM, Angulo FJ, et al. Foodborne illness acquired in the United States—major pathogens. Emerg Infect Dis. 2011;17(1):7-15. doi:10.3201/eid1701.p11101  
3. Scallan E, Griffin PM, Angulo FJ, Tauxe R, Hoekstra RM. Foodborne illness acquired in the United States—unspecified agents. Emerg Infect Dis. 2011;17(1):16-22. doi:10.3201/eid1701.p21101 
4. Delahoy MJ, Shah HJ, Weller DL, et al. Preliminary incidence and trends of infections caused by pathogens transmitted commonly through food — foodborne diseases active surveillance network, 10 U.S. Sites, 2022. MMWR Morb Mortal Wkly Rep. 2023;72:701-706. doi:10.15585/mmwr.mm7226a1 
5. Culture independent diagnostic tests. Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Division of Foodborne, Waterborne, and Environmental Diseases (DFWED). August 10, 2022. Accessed July 12, 2023. https://www.cdc.gov/foodsafety/challenges/cidt.html 
6. Factors that increase your risk for food poisoning. Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Division of Foodborne, Waterborne, and Environmental Diseases (DFWED). July 13, 2023. Accessed July 14, 2023. https://www.cdc.gov/foodsafety/people-at-risk-food-poisoning.html 
7. Tserenpuntsag B, Chang HG, Smith PF, Morse DL. Hemolytic uremic syndrome risk and Escherichia coli O157:H7. Emerg Infect Dis. 2005;11(12):1955-1957. PMID: 16485489. PMCID: PMC3367638. doi:10.3201/eid1112.050607 
8. FoodSafety.gov. Accessed July 14, 2023. https://www.foodsafety.gov/ 
9. Food safety. Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases (NCEZID), Division of Foodborne, Waterborne, and Environmental Diseases (DFWED). September 27, 2022. Accessed July 14, 2023. https://www.cdc.gov/foodsafety/index.html