By Ethan Covey
The incidence of eight domestically acquired infections transmitted commonly through food either increased or remained stable compared with baseline, according to preliminary Foodborne Diseases Active Surveillance Network (FoodNet) data from 2023.
However, a new report hypothesizes that the findings may be caused by an increase in the use of culture-independent diagnostic tests (CIDTs), not by stalled progress against these pathogens (MMWR Morb Mortal Wkly Rep 2024;73[26]:584-593).
“FoodNet’s surveillance efforts are critical for tracking foodborne and enteric illnesses in the U.S.,” said Daniel L. Weller, PhD, an epidemiologist with the CDC’s Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases.
“During 2023, FoodNet expanded its catchment area for the first time since 2004, and it now includes all of Colorado,” Dr. Weller said. “This expansion improved the representativeness of the FoodNet catchment area, and the ability of FoodNet to monitor trends in disease incidence, including the impact of changing diagnostic practices and the generalizability of FoodNet data.”
The 2023 FoodNet catchment area represents 53.6 million people—16% of the U.S. population.
Although Dr. Weller noted that analyses are needed to quantify the representativeness of the FoodNet catchment relative to the U.S. population as a whole, the increased catchment area aids in improving the generalizability of FoodNet data.
The new report found that the incidence of domestically acquired campylobacteriosis, Shiga toxin–producing Escherichia coli infection, yersiniosis, vibriosis and cyclosporiasis increased during 2023. The incidence of listeriosis, salmonellosis and shigellosis also remained stable compared with that from 2016 to 2018, which is used as the baseline for tracking progress toward disease reduction goals.
Use of CIDTs rose during 2023, with 78% of all bacterial infections diagnosed by CIDTs, including 46% diagnosed using only CIDTs.
“Over the past several years, FoodNet’s annual MMWR [report] has noted both a marked increase in incidence for multiple illnesses, and that limited progress has been made toward disease reduction goals,” Dr. Weller said. “CIDTs allow for diagnosis of infections that previously would have gone undetected, and this year’s report highlights that lack of progress toward disease reduction goals might reflect changing diagnostic practices rather than an actual increase in incidence.
“Continued surveillance is needed to monitor the impact of changing diagnostic practices on disease trends,” Dr. Weller said. “Currently, FoodNet is working on a series of analyses to characterize this impact; the first of these analyses, which focused on yersiniosis, was recently published in the Open Forum for Infectious Diseases (2024;11[6]:ofae199). Research is also needed to characterize variability in CIDT adoption across communities and how this may impact our understanding of the epidemiology of illnesses commonly transmitted through food.”
Dr. Weller also stated that future research will aim to address questions raised by the 2023 FoodNet data.
“Increases in CIDT-diagnosed infections are also associated with decreased rates of reflex culture, thereby reducing the number of isolates available for subtyping, whole-genome sequencing and antimicrobial resistance characterization,” he said. “The relative impact of this reduction for each species, serotype or serogroup, as well as antimicrobial resistant infections needs to be investigated. Overall, these findings highlight the need for culture-independent approaches for speciation, subtyping and characterization of antimicrobial resistance.”
