Preliminary Incidence and Trends of Infections with Pathogens Transmitted Commonly Through Food - Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2016-2019.

To evaluate progress toward prevention of enteric illnesses, the Foodborne Diseases Active Surveillance Network (FoodNet) of CDC's Emerging Infections Program monitors the incidence of laboratory-diagnosed infections caused by eight pathogens transmitted commonly through food at 10 U.S. sites.* This report summarizes preliminary 2019 data and describes changes in incidence compared with that during 2016-2018. The incidence of enteric infections caused by these eight pathogens reported by FoodNet sites in 2019 continued to increase or remained unchanged, indicating progress in controlling major foodborne pathogens in the United States has stalled. Campylobacter and Salmonella caused the largest proportion of illnesses; trends in incidence varied by Salmonella serotype. Widespread adoption of whole genome sequencing (WGS) of bacteria has improved the ability to identify outbreaks, emerging strains, and sources of pathogens. To maximize the potential of WGS to link illnesses to particular sources, testing of isolates by clinical and public health laboratories is needed. Reductions in Salmonella serotype Typhimurium suggest that targeted interventions (e.g., vaccinating chickens and other food animals) might decrease human infections. Reducing contamination during food production, processing, and preparation will require more widespread implementation of known prevention measures and of new strategies that target particular pathogens and serotypes.

To evaluate progress toward prevention of enteric illnesses, the Foodborne Diseases Active Surveillance Network (FoodNet) of CDC's Emerging Infections Program monitors the incidence of laboratory-diagnosed infections caused by eight pathogens transmitted commonly through food at 10 U.S. sites.* This report summarizes preliminary 2019 data and describes changes in incidence compared with that during 2016-2018. The incidence of enteric infections caused by these eight pathogens reported by FoodNet sites in 2019 continued to increase or remained unchanged, indicating progress in controlling major foodborne pathogens in the United States has stalled. Campylobacter and Salmonella caused the largest proportion of illnesses; trends in incidence varied by Salmonella serotype. Widespread adoption of whole genome sequencing (WGS) of bacteria has improved the ability to identify outbreaks, emerging strains, and sources of pathogens. To maximize the potential of WGS to link illnesses to particular sources, testing of isolates by clinical and public health laboratories is needed. Reductions in Salmonella serotype Typhimurium suggest that targeted interventions (e.g., vaccinating chickens and other food animals) might decrease human infections. Reducing contamination during food production, processing, and preparation will require more widespread implementation of known prevention measures and of new strategies that target particular pathogens and serotypes.
Members of FoodNet conduct active, population-based surveillance for laboratory-diagnosed infections caused by Campylobacter, Cyclospora, Listeria, Salmonella, Shiga bacterial infection is a positive CIDT result not confirmed by culture. ¶ Listeria infections are defined as isolation of L. monocytogenes or detection of its nucleic acid sequences from a normally sterile site, or from placental or fetal tissue in the instance of miscarriage or stillbirth. Cyclospora infections are defined as detection of the parasite by microscopy using ultraviolet fluorescence or specific stains or by polymerase chain reaction. Cases with no documentation of international travel or unknown travel are considered domestically acquired infections.** The patient's disposition at hospital discharge, or 7 days after specimen collection if not hospitalized, is attributed to the infection.
Incidence per 100,000 population was calculated by dividing the number of infections in 2019 by the U.S. Census estimates of the surveillance area population for 2018. Incidence measures include all laboratory-diagnosed infections. A negative binomial model with 95% confidence intervals (CIs) was used to estimate change in incidence during 2019 compared with that during 2016-2018, adjusting for changes in the population over time; CIs not including zero were considered statistically significant. Analyses were performed using SAS statistical software (version 9.4; SAS Institute).
Surveillance for physician-diagnosed post-diarrheal hemolytic uremic syndrome (HUS), a complication of STEC ¶ Serogroup or serotype is only available for infections confirmed by culture. ** No international travel or not known if international travel occurred within 30 days before illness onset for Listeria, Salmonella serotypes Typhi and Paratyphi, 15 days for Cyclospora, and 7 days for all other pathogens.
infection characterized by renal failure, thrombocytopenia, and microangiopathic anemia, is conducted by reviewing hospital discharge data and by working with a network of nephrologists and infection preventionists. This report includes HUS data for children for 2018, the most recent year for which data are available.

Discussion
In 2019, compared with the previous 3 years, the incidence of infections caused by pathogens transmitted commonly through food increased (for Campylobacter, Cyclospora, STEC, Vibrio, Yersinia) or remained unchanged (for Listeria, Salmonella,  Shigella). These data indicate that Healthy People 2020 targets for reducing foodborne illness will not be met. The identification of infections that might not have been detected before adoption of CIDTs cannot explain this overall lack of progress. Better implementation of known prevention approaches and new strategies is needed to overcome the continued challenges to reducing foodborne illnesses.
Serotype Enteritidis has been the most common cause of Salmonella infections at FoodNet sites since 2007 and incidence has not decreased. Eggs were the major source of Enteritidis infections in the 1980s (1). Chicken was recognized as another important source during the late 1990s (2,3). Infantis moved from the ninth most common Salmonella serotype among infected persons during 1996-1998 to the sixth most common in 2019. Many infections are now caused by a new, highly resistant strain found in chicken (4,5). The incidence of some serotypes has declined. Typhimurium moved from the most common serotype during 1996-1998 to the third most common in 2019. Heidelberg, the third most common serotype during 1996-1998, is no longer among the top 20. These decreases might be partly related to the widespread practice of vaccinating chickens against Typhimurium, which shares antigens with Heidelberg (6). This observation, combined with a marked decline in Enteritidis infections in the United Kingdom after implementation of widespread chicken vaccination and improved farm hygiene (7), suggests that targeting other serotypes through poultry vaccination could be one way to reduce human illnesses in the United States.
Laboratory-diagnosed non-O157 STEC infections continue to increase. Although STEC O157 infections appear to be decreasing, outbreaks linked to leafy greens continue (8). Produce is also an important source for Cyclospora, Listeria, and Salmonella (9,10). Although adoption of syndromic panels † † could be contributing to the large increase in Cyclospora, increased exposure to this pathogen cannot be excluded. Continued implementation of FDA's Produce Safety Rule § § (e.g., expanded surveillance inspections of foreign † † Syndromic panels are commercial CIDTs that simultaneously detect multiple pathogens associated with clinical syndromes, such as diarrheal illness. § § https://www.fda.gov/Food/GuidanceRegulation/FSMA/ucm334114.htm.

Summary
What is already known about this topic?
The incidence of most infections transmitted commonly through food has not declined for many years.
What is added by this report?
Incidence of infections caused by Listeria, Salmonella, and Shigella remained unchanged, and those caused by all other pathogens reported to FoodNet increased during 2019. Infections caused by Salmonella serotype Enteritidis, did not decline; however, serotype Typhimurium infections continued to decline.
What are the implications for public health practice?
New strategies that target particular serotypes and more widespread implementation of known prevention measures are needed to reduce Salmonella illnesses. Reductions in Salmonella serotype Typhimurium suggest that targeted interventions (e.g., vaccinating chickens and other food animals) might decrease human infections. Isolates are needed to subtype bacteria so that sources of illnesses can be determined. and domestically grown produce) is needed, as are innovative approaches for preventing contamination.
Advances in laboratory science continue to revolutionize enteric disease clinical diagnostics and surveillance. Many laboratories now use CIDTs to detect infections that would have previously been undiagnosed. In 2019, public health laboratories fully transitioned the standard subtyping method for clinical bacterial isolates from pulsed-field gel electrophoresis to WGS. WGS provides detailed information to more effectively recognize outbreaks, determine resistance patterns, and investigate reoccurring, emerging, and persisting strains. However, because CIDTs do not yield isolates needed to perform WGS, the full potential of these new technologies can only be realized when laboratories are fully able to culture CIDT-positive specimens.
The findings in this report are subject to at least three limitations. First, part of the observed increase in incidence is likely due to increased use of CIDTs that identify previously unrecognized infections. Changes in clinicians' ordering practices and varying test sensitivities and specificities might also contribute to this observation. Second, changes in health care-seeking behavior, access to health services, or other population characteristics might have changed. Finally, year-to-year changes in incidence might not reflect sustained trends.
The landscape of foodborne disease continues to change, as do the methods to determine the incidence and sources of these infections. FoodNet surveillance data indicate that progress in controlling major foodborne pathogens in the United States has stalled. To better protect the public and achieve forthcoming Healthy People 2030 foodborne disease reduction goals, more widespread implementation of known prevention measures and new strategies that target particular pathogens and serotypes are needed.