The 26% decrease in incidence of infections caused by pathogens transmitted commonly through food during 2020 was the largest single-year variation in incidence during 25 years of FoodNet surveillance; widespread public health interventions implemented to prevent SARS-CoV-2 transmission might have contributed to this decrease. For example, infections associated with international travel decreased markedly after pandemic-related travel restrictions were imposed. Other interventions, such as restaurant closures, might have contributed to declines in incidence. However, a higher than usual proportion of infections might have been undetected because factors such as changes in health care-seeking behaviors, and broader use of telehealth might have limited the number of stool specimens tested. Marked decreases in emergency department visits for abdominal pain and other digestive or abdominal signs and symptoms occurred early in the pandemic. The proportion of infections resulting in hospitalization increased slightly; possible explanations include disproportionate decreases in health care-seeking among those with milder illness or delayed health care-seeking resulting in more severe illness at the time of clinical presentation.
The proportion of infections diagnosed by culture versus CIDTs was stable during 2020, suggesting that a change in clinical laboratory testing practices was not a major contributor to the decreased incidence of infections. Before 2020, the incidence of Campylobacter, Salmonella, STEC, Vibrio, Yersinia, and Cyclospora infections had been increasing; the addition of infections diagnosed by CIDTs to FoodNet surveillance beginning in 2012, and the introduction of DNA-based syndrome panels§§ in 2016 likely contributed to the increases.
Changes in clinical and public health laboratory capacity in response to the COVID-19 pandemic might have contributed to observed decreases in reflex culturing. Before 2020, reflex culture of specimens positive for Campylobacter, Salmonella, Shigella, and Yersinia increased in FoodNet sites, augmented by CDC funding. Until metagenomic CIDTs are developed, culture is necessary to identify pathogen subtypes, antimicrobial resistance patterns, and whole-genome sequences. Fewer cultures decrease the ability to detect and investigate outbreaks and sporadic cases of emerging pathogens, which relies on sequencing.
The incidences of Salmonella Infantis, Cyclospora, and Yersinia infections, which had previously been increasing, did not change, possibly because of continuing prepandemic factors that led to rising incidences during previous years; the stable incidences despite the pandemic suggest that they might have increased otherwise. As pandemic-related restrictions are lifted, illnesses caused by these pathogens and by Hadar, the one Salmonella serotype with increasing incidence, should be closely monitored. Rising multidrug resistant Salmonella Infantis infections have been linked to consumption of chicken.[6–8] Hadar infections have been linked to backyard flocks and to consumption of turkey.[8,9] USDA-FSIS did not detect a significantly higher percentage of Salmonella Hadar in raw poultry samples collected in 2020 compared with 2017–2019 (USDA-FSIS, unpublished data, 2021). Typhimurium continued to decline in rank among Salmonella serotypes, dropping to fourth most common for the first time.
The findings in this report are subject to at least three limitations. First, the pandemic and corresponding public health response make explaining changes in the observed incidences of infections challenging. Second, changes in health care-seeking behaviors and health care delivery during the pandemic likely limited ascertainment of cases. Finally, sites reported decreases that varied over time in the willingness of ill persons to be interviewed and in staff member capacity to conduct case interviews; these factors might have resulted in missing data and recall bias.
Public health interventions to prevent SARS-CoV-2 transmission likely influenced exposures associated with enteric diseases, resulting in real declines in incidence, as evidenced by decreased numbers of infections associated with international travel. Continued surveillance might improve the understanding of how the pandemic affected foodborne illness and might help identify prevention measures and strategies that target particular pathogens and foods. To reduce the incidence of these infections concerted efforts are needed, from farm to processing plant to restaurants and homes. Consumers can reduce their risk of foodborne illness by following safe food-handling and preparation recommendations.
Workgroup members, Foodborne Diseases Active Surveillance Network, Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC; Emerging Infections Program, Division of Preparedness and Emerging Infections, National Center for Emerging and Zoonotic Infectious Diseases, CDC; Robert Breazu, Staci Dixon, Brian Katzowitz, Daneisha Hawkins, Carey Devine, Stacey Riddick, Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC.
Morbidity and Mortality Weekly Report. 2021;70(38):1332-1336. © 2021 Centers for Disease Control and Prevention (CDC)