Preliminary Incidence and Trends of Infections with Pathogens Transmitted Commonly Through Food — Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2015–2018

Foodborne diseases represent a major health problem in the United States. The Foodborne Diseases Active Surveillance Network (FoodNet) of CDC's Emerging Infections Program monitors cases of laboratory-diagnosed infection caused by eight pathogens transmitted commonly through food in 10 U.S. sites.* This report summarizes preliminary 2018 data and changes since 2015. During 2018, FoodNet identified 25,606 infections, 5,893 hospitalizations, and 120 deaths. The incidence of most infections is increasing, including those caused by Campylobacter and Salmonella, which might be partially attributable to the increased use of culture-independent diagnostic tests (CIDTs). The incidence of Cyclospora infections increased markedly compared with 2015-2017, in part related to large outbreaks associated with produce (1). More targeted prevention measures are needed on produce farms, food animal farms, and in meat and poultry processing establishments to make food safer and decrease human illness.

* Connecticut, Georgia, Maryland, Minnesota, New Mexico, Oregon, Tennessee, and selected counties in California, Colorado, and New York (https://www. cdc.gov/foodnet). † STEC cases are defined as identification of Shiga toxin or its genes by any laboratory; it is not possible to distinguish among serogroups using CIDTs. are attributed to the infection, as is the patient's vital status at hospital discharge, or 7 days after specimen collection if the patient was not hospitalized.
Incidence per 100,000 population was calculated by dividing the number of infections in 2018 by U.S. Census estimates of the surveillance area population for 2017. A negative binomial model with 95% confidence intervals (CIs) was calculated using SAS (version 9.4; SAS Institute) to estimate changes in incidence.
Surveillance for physician-diagnosed postdiarrheal hemolytic uremic syndrome, a complication of STEC infection characterized by renal failure, thrombocytopenia, and microangiopathic anemia, is conducted through a network of nephrologists and infection preventionists and by hospital discharge data review. This report includes pediatric hemolytic uremic syndrome cases (those occurring in persons aged <18 years) identified during 2017, the most recent year for which data are available.

Discussion
Campylobacter has been the most commonly identified infection in FoodNet since 2013. It causes diarrhea, sometimes bloody, and 18% of persons are hospitalized. A rare outcome of Campylobacter infection is Guillain-Barré syndrome, a type of autoimmune-mediated paralysis. Poultry is a major source of Campylobacter (2). In August 2018, FSIS began using a new testing method; in a study of that method, Campylobacter was isolated from 18% of chicken carcasses and 16% of chicken parts sampled (3). FSIS currently makes aggregated test results available and intends to update performance standards for Campylobacter contamination.
The incidence of infections with Enteritidis, the most common Salmonella serotype, has not declined in over 10 years. Enteritidis is adapted to live in poultry, and eggs are an important source of infection (4). By 2012, FDA had implemented the Egg Safety Rule, ¶ which requires preventive measures during the production of eggs in poultry houses and requires subsequent refrigeration during storage and transportation, for all farms with ≥3,000 hens. In 2018, a multistate outbreak of Enteritidis infections was traced to eggs from a farm that had not implemented the required egg safety measures after its size reached ≥3,000 hens (5). Chicken meat is also an important source of Enteritidis infections (4). In December 2018, FSIS reported that 22% of establishments that produce chicken parts failed to meet the Salmonella performance standard (USDA-FSIS Salmonella verification testing program**). The percentage of samples of chicken meat and intestinal contents that yielded Enteritidis were similar in 2018 to those during 2015-2017 (USDA-FSIS, unpublished data). In contrast, a decline in serotype Typhimurium isolated from the same sources was observed during the same period. This trend coincides with declines in Typhimurium human illnesses. Changes in poultry production practices, including vaccination against Typhimurium, might have resulted in these declines (6). In the United Kingdom, vaccination of both broiler and layer chickens against Enteritidis, along with improved hygiene, ¶ h t t p s : / / w w w . f d a . g o v / F o o d / G u i d a n c e R e g u l a t i o n / GuidanceDocumentsRegulatoryInformation/Eggs/ucm170615.htm. ** https://www.fsis.usda.gov/wps/portal/fsis/topics/data-collection-and-reports/ microbiology/salmonella-verification-testing-program.

Summary
What is already known about this topic?
The incidence of foodborne infections has remained largely unchanged. Clinical laboratories are increasingly using cultureindependent diagnostic tests (CIDTs) to detect enteric infections. CIDTs benefit public health surveillance by identifying pathogens not routinely detected by previous methods but complicate data interpretation.
What is added by this report?
The incidence of most infections increased during 2018 compared with 2015-2017; this might be partially attributable to increased CIDT use. The incidence of Cyclospora infections increased markedly, in part related to large outbreaks associated with produce. The number of human infections caused by Campylobacter and Salmonella, especially serotype Enteritidis, remains high.
What are the implications for public health practice?
As use of CIDTs increases, it is important to obtain and subtype isolates and interview ill persons to monitor prevention efforts and develop more targeted prevention and control measures to make food safer and decrease human illness.
was followed by a marked decrease in human Enteritidis infections (7). Produce is a major source of foodborne illnesses (2). During 2018, romaine lettuce was linked to two multistate outbreaks of STEC O157 infections (8). The marked increase in reported Cyclospora infections was likely attributable to several factors including produce outbreaks and continued adoption of DNA-based syndrome panel tests (1). Improved agricultural practices are needed to prevent produce-associated infections. FDA provides technical assistance to task forces created by the produce industry, to determine how to prevent contamination of romaine lettuce and facilitate outbreak investigations by improving product labeling and traceability. In 2018, FDA expanded surveillance sampling of foreign and domestically grown produce to assess its safety (9). FDA is implementing the Produce Safety Rule, † † with routine inspections of large produce farms planned this spring. Because produce is a major component of a healthy diet and is often consumed raw, making it safer is important for improving human health (10).
The findings in this report are subject to at least three limitations. First, the changing diagnostic landscape makes interpretation of incidence and trends more complex. Increases in † † https://www.fda.gov/Food/GuidanceRegulation/FSMA/ucm334114.htm. reported incidence might be attributable entirely, or in part, to changes in clinician ordering practices, increased use of DNAbased syndrome panels that identify pathogens not routinely captured by traditional methods, and changes in laboratory practices in response to the availability of these panels. Second, some CIDT results might be false positives. Finally, year-toyear variations, attributable in part to large outbreaks, might not indicate sustained trends.
The need to obtain and subtype isolates from ill persons is becoming an increasing burden to state health departments but is critical for maintaining surveillance to detect and investigate outbreaks, evaluating prevention efforts, and developing targeted control measures. Measures that might decrease foodborne illnesses include enhanced efforts targeting Campylobacter contamination of chicken; strengthening prevention measures during egg production, especially within small flocks; vaccinating poultry against Salmonella serotype Enteritidis; decreasing Salmonella contamination of produce, poultry, and meat; and continued implementation of the Food Safety Modernization Act, specifically FDA's Produce Safety Rule. FoodNet continues to collect data and develop analytic tools to adjust for changes in diagnostic testing practices and test characteristics. These actions, along with FoodNet's robust surveillance, provide data to help evaluate the effectiveness of prevention efforts and determine when additional measures are needed.