The incidence of infections transmitted commonly through food has remained largely unchanged for many years. Culture-independent diagnostic tests (CIDTs) are increasingly used by clinical laboratories to detect enteric infections. CIDTs benefit public health surveillance by identifying illnesses caused by pathogens not captured routinely by previous laboratory methods.
Decreases in incidence of infection of Shiga toxin–producing Escherichia coli (STEC) O157 and Salmonella serotypes Typhimurium and Heidelberg have been observed over the past 10 years. These declines parallel findings of decreased Salmonella contamination of poultry meat and decreased STEC O157 contamination of ground beef.
As use of CIDTs continues to increase, higher, more accurate incidence rates might be observed. However, without isolates, public health laboratories are unable to subtype pathogens, determine antimicrobial susceptibility, and detect outbreaks. Further prevention measures are needed to decrease the incidence of infection by pathogens transmitted commonly through food.
Despite ongoing food safety measures in the United States, foodborne illness continues to be a substantial health burden. The 10 U.S. sites of the Foodborne Diseases Active Surveillance Network (FoodNet)* monitor cases of laboratory-diagnosed infections caused by nine pathogens transmitted commonly through food. This report summarizes preliminary 2017 data and describes changes in incidence since 2006.
In 2017, FoodNet reported 24,484 infections, 5,677 hospitalizations, and 122 deaths. Compared with 2014–2016, the 2017 incidence of infections with Campylobacter, Listeria, non-O157 Shiga toxin–producing Escherichia coli (STEC), Yersinia, Vibrio, and Cyclospora increased. The increased incidences of pathogens for which testing was previously limited might have resulted from the increased use and sensitivity of culture-independent diagnostic tests (CIDTs), which can improve incidence estimates (1). Compared with 2006–2008, the 2017 incidence of infections with Salmonella serotypes Typhimurium and Heidelberg decreased, and the incidence of serotypes Javiana, Infantis, and Thompson increased. New regulatory requirements that include enhanced testing of poultry products for Salmonella† might have contributed to the decreases.
The incidence of STEC O157 infections during 2017 also decreased compared with 2006–2008, which parallels reductions in isolations from ground beef.§ The declines in two Salmonella serotypes and STEC O157 infections provide supportive evidence that targeted control measures are effective. The marked increases in infections caused by some Salmonella serotypes provide an opportunity to investigate food and nonfood sources of infection and to design specific interventions.
FoodNet conducts active, population-based surveillance for laboratory-diagnosed infections caused by Campylobacter, Cryptosporidium, Cyclospora, Listeria, Salmonella, STEC, Shigella, Vibrio, and Yersinia in 10 sites that account for approximately 15% of the U.S. population (an estimated 49 million persons in 2016). FoodNet is a collaboration among CDC, 10 state health departments, the U.S. Department of Agriculture’s Food Safety and Inspection Service (USDA-FSIS), and the Food and Drug Administration (FDA). Laboratory-diagnosed bacterial infections are defined as isolation of bacteria from a clinical specimen by culture or detection by a CIDT. CIDTs detect bacterial antigens, nucleic acid sequences, or, for STEC, Shiga toxin or Shiga toxin genes.¶ A CIDT-positive–only bacterial infection is a positive CIDT result without culture confirmation. Listeria cases are defined as isolation of L. monocytogenes or detection by a CIDT from a normally sterile site or from placental or fetal tissue in the instance of miscarriage or stillbirth. Laboratory-diagnosed parasitic infections are defined as detection of the parasite from a clinical specimen. Hospitalizations and deaths within 7 days of specimen collection are attributed to the infection. Surveillance for physician-diagnosed postdiarrheal hemolytic uremic syndrome (HUS) is conducted through a network of nephrologists and infection preventionists and hospital discharge data review. This report includes pediatric HUS cases identified during 2016, the most recent year for which data are available.
Incidence per 100,000 population was calculated by dividing the number of infections in 2017 by the U.S. Census estimates of the surveillance area population for 2016. Incidence measures include all laboratory-diagnosed infections reported. A negative binomial model with 95% confidence intervals (CIs) was used to estimate change in incidence during 2017 compared with that during 2014–2016 and 2006–2008. Because of large changes in testing practices since 2006, incidence comparisons with 2006–2008 used only culture-confirmed bacterial infections, and comparisons with 2014–2016 used culture-confirmed and CIDT-positive–only cases combined. For HUS, 2016 incidence was compared with that during 2013–2015.
Preliminary incidence and trends of infections with pathogens transmitted commonly through food-foodborne diseases active surveillance network, 10 U.S. sites, 2006-2017
Workgroup members, Foodborne Diseases Active Surveillance Network (FoodNet), Emerging Infections Program, CDC; Brittany Behm, Staci Dixon, Elizabeth Greene, Logan Ray, Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC; Neal Golden, Steven Mamber, and Joanna Zablotsky Kufel, U.S. Department of Agriculture’s Food Safety and Inspection Service.