FoodNet 2018 Preliminary Data

Documenting the major sources of and trends in foodborne illness provides important information needed to determine whether prevention measures are working. Each year, FoodNet reports on the number of infections in the FoodNet surveillance area from pathogens transmitted commonly through food. Laboratory tests, including cultures for bacteria and culture-independent diagnostic tests (CIDTs), detected these pathogens.

This year’s report summarizes 2018 preliminary surveillance data and describes 2018 incidence data compared with  2015–2017 data for infections caused by Campylobacter, Cyclospora, Listeria, Salmonella, Shiga toxin-producing Escherichia coli (STEC), Shigella, Vibrio, and Yersinia. The report also summarizes cases of hemolytic uremic syndrome (HUS) for 2017.

Key Findings from 2018 Surveillance Data

  • Campylobacter infection has been the most commonly identified infection in FoodNet sites since 2013, and the incidence appears to be increasing.
    • Poultry is a major source of Campylobacter bacteria.
  • Salmonella infection is the second most common infection, and the incidence has not declined compared with the previous 3 years. The three most common Salmonella serotypes were Enteritidis, Newport, and Typhimurium.
    • Enteritidis infections have not declined in more than 10 years, despite regulatory programs intended to reduce Salmonella in chicken and eggs, both of which are important sources.
  • The incidence of Cyclospora infections increased markedly, in part because of large outbreaks associated with produce, a major source of foodborne illnesses.
  • The number of infections diagnosed by CIDTs increased 65% compared with the previous 3 years; the increase ranged from 29% for STEC to 311% for Vibrio.
    • Culture was attempted on 75% of specimens with a positive CIDT result; 71% of specimens cultured were positive.
    • Culture provides critical information to detect outbreaks, identify sources of contamination, inform treatment, and target control measures.

Interpreting Changes in Incidence of Infections

More infections are being diagnosed, probably because laboratories are using CIDTs more often. It also is possible that the number of infections is truly increasing.

To reduce infections, we first need to know how people are getting infected. These infections come from many sources, most often from chicken. People can get infected when chicken is undercooked and when Campylobacter in raw chicken or its juices contaminates hands, other foods, or kitchen equipment. Focusing on interventions throughout the food production chain that reduce Campylobacter bacteria in chicken could lead to fewer illnesses in people. Whole genome sequencing might help us figure out the contribution of various sources and help target interventions. FoodNet tracks illnesses to see if prevention measures are working.

Chicken is often contaminated with harmful germs, such as Campylobacter and Salmonella.

package of raw chicken

Restaurants and consumers should take special care when handling and preparing this food, including keeping raw chicken separate from foods that won’t be cooked before they are eaten, to avoid cross-contamination.

If chicken is on your menu, follow CDC’s tips when shopping, cooking, and eating out >

More infections are being diagnosed, probably because laboratories are using CIDTs more often. However, it’s clear that infections are not decreasing, so more prevention measures are needed.

Many serotypes of Salmonella bacteria exist and their sources vary, so the best interventions vary by serotype. Overall incidence of infections could be decreased by focusing prevention measures on Enteritidis and other common serotypes, on chicken, and on produce consumed raw.

Whole genome sequencing can help identify specific sources of illnesses. FoodNet tracks illnesses to determine if prevention measures are working.

More laboratories are using DNA-based syndrome panel tests for Cyclospora than in past years, so we are finding more infections. It’s also possible that the number of infections was truly higher, in part driven by outbreaks in 2018.

In 2018, the incidence of STEC infections increased 26% compared with 2015–2017. The increased incidence was driven by an increase in the number of non-O157 STEC infections diagnosed, probably related to increased use of CIDTs.

STEC are classified by serogroup; the most common is O157. Knowing the serogroup can help identify the source of infection and inform treatment options. Clinical laboratories have been able to test stool samples for O157 for decades. With the increasing use of CIDTs, clinical laboratories now commonly determine if a specimen contains a Shiga toxin, and then test the specimen for O157. If they do not find O157, they assume a non-O157 STEC is present. They can then send the specimen to a specialized laboratory to determine which non-O157 STEC serogroup is present.

Antibiotics are not recommended for patients with suspected STEC infections until complete diagnostic tests find no evidence of STEC infection.

Vibrio infections have been increasing for many years. Warming of coastal waters, which contributes to growth and persistence of Vibrio bacteria, has been proposed as a factor. The increase in Vibrio infections in the past few years might be due, in part, to more laboratories testing for Vibrio and more infections being diagnosed. In the past, testing for this organism was limited, and infections may have been undiagnosed. CIDTs are easier to perform than traditional culture methods and are becoming widely used to diagnose Vibrio infections. Also, a portion of these infections may be false positives as the media used to transport stool samples has sometimes contained fragments of Vibrio bacteria that CIDTs can detect.

The increase in Yersinia infections is likely due to a great extent to more laboratories testing for Yersinia using CIDTs, and so more infections are being diagnosed. Yersinia is difficult to culture. In the past, testing for this organism was limited, and infections may have been underdiagnosed. It is also possible that some results are false positives.

Questions and Answers About CIDTs

CIDTs detect the presence of a specific antigen or genes of an organism, such as Salmonella. These tests do not require laboratories to grow living organisms (a process known as culturing). Therefore, CIDTs can yield results far sooner than cultures can.

Because CIDTs are fast and easy to use, they detect some illnesses that would have otherwise been missed. However, CIDTs do not provide certain information needed to characterize organisms. For example, CIDTs currently can detect Salmonella, but cannot identify the Salmonella serotype that caused the infection.

To counter these limitations, laboratories can culture specimens after a CIDT is positive (a practice called reflex culturing), and CIDT manufacturers can create new tests to provide information that is now available only from cultured specimens.

Each year, FoodNet publishes a summary of surveillance data and trends information in CDC’s Morbidity and Mortality Weekly Report (MMWR). Recent changes in diagnostic practices challenge our ability to monitor disease trends. Because CIDTs are increasingly used for diagnosis, and positive results likely indicate true infections, FoodNet includes CIDT-positive results in counts of numbers of infections. However, more data are needed to understand how CIDTs have affected surveillance. For example, FoodNet is collecting data on the changes in number of people tested and on the accuracy of CIDTs as well as developing new analytic techniques to better assess trends in diagnosed infections.

Questions and Answers About Food Safety

Since 1996, FoodNet has been counting cases and tracking trends for infections transmitted commonly through food. Information gathered on which illnesses are decreasing and which are increasing provides a foundation for food safety policy and prevention efforts. FoodNet’s surveillance data, such as those in this report, show where efforts are needed to reduce foodborne illnesses. Learn more about FoodNet >

CDC uses the best scientific methods and information available to monitor, investigate, control, and prevent foodborne illness. Using epidemiology and laboratory science, CDC assesses public health threats. CDC works closely with state health departments to monitor the frequency of specific diseases and to conduct national surveillance for the diseases it monitors.

When food safety threats appear, CDC collaborates with public health partners, including state health departments, the U.S. Food and Drug Administration (FDA), and the U.S. Department of Agriculture (USDA), to conduct epidemiologic and laboratory investigations to determine the causes of these threats and how they can be controlled. Although CDC does not regulate the safety of food, CDC works with regulatory agencies to guide food safety policies and assess the effectiveness of current prevention efforts. CDC provides independent scientific assessment of what the problems are, how they can be controlled, and where the gaps exist in our knowledge. You can find more information on foodborne illness and CDC’s prevention activities on CDC’s Food Safety website.

Government regulation related to food safety is the responsibility of FDA, USDA’s Food Safety and Inspection Service (USDA-FSIS), the National Marine Fisheries Service, and other regulatory agencies.

Recent regulatory efforts include the following:

  • FDA is continuing to implement the FDA Food Safety Modernization ActExternal, which establishes science and risk-based standards for the production and transportation of human and animal food, outlining specific actions that industry must take at different points of the supply chain to prevent contamination.
    • Inspections of large produce farms have begun in spring 2019.
    • In response to recent outbreaks and as part of continued implementation of the Produce Safety Rule, FDA has expanded surveillance sampling of foreign and domestically grown produce.
  • USDA-FSIS’ New Poultry Inspection System reduces the risk of foodborne illness by focusing FSIS inspection activities on those that are more effective in ensuring food safety.
  • Each month, USDA-FSIS updates the individual establishment Salmonella performance standard category informationExternal for raw poultry carcasses, raw chicken parts, and comminuted Cdc-pdf[PDF – 16 pages]External poultry products.
    • Each month, FSIS posts the aggregate sampling resultsExternal showing the number of establishments that achieve, meet, or exceed the maximum allowable percent positive for establishments producing young chicken or turkey carcasses, raw chicken parts, or not ready-to-eat (NRTE) comminuted poultry products.
  • USDA-FSIS intends to update performance standards for Campylobacter contamination of raw poultry.
  • USDA-FSIS intends to update Salmonella performance standards for raw ground beef and make new standards for beef manufacturing trimmings, a component of ground beef.

CDC works closely with regulatory agencies as they, along with industry, develop and implement measures to make our food safer.

Suggested citation: Centers for Disease Control and Prevention (CDC). Preliminary Incidence and Trends of Infections with Pathogens Transmitted Commonly Through Food — Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2015–2018. MMWR Morb Mortal Wkly Rep. 2019 April 26.