U.S. Department of Agriculture
Food Safety and Inspection Service
Washington, DC 20250

Report to Congress

FoodNet: An Active Surveillance System for
Bacterial Foodborne Diseases in the United States

April 1998



Overview of FoodNet

Foodborne Illness Data

Tables 1-4

Table 1: Percent Pathogen by Site

Table 2: Percent Site by Pathogen

Table 3: Cases per 100,000 by Pathogen for all Sites (1996 vs. 1997)

Table 4: Pathogen by Month -- All Sites

Chart 1: Pathogen by Month--All Sites

Tables 5-7

Table 5: Age Distribution by Pathogen for all Sites

Table 6: Sex Distribution by Pathogen for all Sites

Table 7: Patient Outcome by Pathogen for all Sites


The U.S. Department of Agriculture has been directed by Congress to provide an annual report on the incidence of foodborne illness in the United States. This report is to be submitted to the House and Senate Committees on Appropriations.

This report includes a description of the Foodborne Diseases Active Surveillance Network (FoodNet) and data on the incidence of foodborne illness for calendar year 1997. Data already collected are being analyzed by The Centers for Disease Control and Prevention and the seven surveillance sites.

Questions about this report or about FSIS may be directed to the Food Safety and Inspection Service, U.S. Department of Agriculture, Washington, D.C. 20250.

Overview of Foodnet

The Food Safety and Inspection Service (FSIS) of the U. S. Department of Agriculture (USDA) administers a comprehensive system of inspection laws to ensure that meat, poultry, and egg products moving in interstate and foreign commerce for use as human food are safe, wholesome, and accurately labeled.

Over the past decade, foodborne illnesses caused by bacterial contamination have heightened concern about the safety of food. The Centers for Disease Control and Prevention (CDC) has identified bacterial pathogens as the most common cause of foodborne illnesses because they can be easily transmitted and multiply rapidly in food, thus making them difficult to control. CDC has targeted seven bacterial foodborne pathogens (Campylobacter, E. coli O157:H7, Listeria, Salmonella, Shigella, Vibrio, and Yersinia) as those of greatest concern to public health. Government economists have estimated that foodborne illnesses cost billions of dollars each year in lost productivity and medical care. However, an accurate picture of both the number and causes of foodborne illnesses in the United States is unknown.

In July 1995, as part of the federal government's campaign to improve the safety of the nation's food supply, FSIS began a collaborative project with CDC and the Food and Drug Administration, known originally as the Sentinel Site Study and more recently as the Foodborne Diseases Active Surveillance Network or FoodNet, to collect more precise information on the incidence of foodborne disease in the United States. This project includes direct working links with state and local health departments at seven selected sites nationwide as a means of obtaining the most complete and current data about foodborne illness possible. This study, which is expected to continue for several years, will provide much-needed baseline data regarding the incidence of foodborne illness in the United States which is attributable to the consumption of meat, poultry, and other food products.


Bacterial foodborne diseases are currently reported to local and state health departments and CDC through passive surveillance systems. As with all passive systems, cases are frequently under-reported. In fact, only 1% to 5% of foodborne disease cases are believed to be reported to CDC through passive surveillance systems.

In July 1994, the USDA Pathogen Reduction Task Force recommended that FSIS work with CDC on research and surveillance activities that will better characterize risks for foodborne pathogens. This recommendation echoed a National Academy of Sciences recommendation for more community-based surveillance of foodborne disease. To improve data on the incidence and causes of foodborne illness, FDA, FSIS and CDC have established seven sites to study the epidemiologic association between sporadic cases of foodborne illness and the preparation and consumption of meat, poultry, and egg products. The seven selected sites are Northern California, Oregon, Minnesota, Connecticut, and counties in northern Georgia, eastern Maryland, and western New York.


The major objectives of FoodNet are to:

  • determine the yearly incidence of illness due to seven bacterial foodborne pathogens (i.e., Campylobacter, E. coli O157:H7, Listeria, Salmonella, Shigella, Vibrio, and Yersinia);

  • develop a network to collaboratively respond to emerging foodborne diseases;

  • determine the proportion of foodborne disease cases attributed to specific food commodities; and

  • determine whether federal interventions (such as HACCP) are having a measurable effect on the incidence of foodborne illness attributable to consumption of meat, poultry, and other foods.

Scope and Duration of Study

FoodNet is a comprehensive effort to track major pathogens that cause sporadic foodborne illness, and to explore what associations may exist between cases and the types of food products consumed.

For the project to be most successful, data must be collected over a number of years in order to chart trends and evaluate the effectiveness of control strategies. FoodNet will also be used as a national laboratory for surveillance strategies which will be useful in all states to more precisely determine the extent and causes of foodborne illness.

Components of FoodNet

  • Active Surveillance: The purpose of this survey is to determine in each site the actual number of laboratory-confirmed cases of illness caused by the seven targeted bacteria and, as of 1997, two targeted parasites.

    • Bacterial:  In 1997, the total population under surveillance was 15.9 million persons (using 1996 Census data). Culture-confirmed cases for the five sites total 8,031. The Tables in the last section provide detailed information about these cases.

    • Parasitic:  In 1997, data collection began in four sites for illnesses caused by the parasites Cryptosporidium and Cyclospora. The total population under surveillance was 20.9 million persons (using 1996 Census data). A total of 517 cases were found. Beginning in January 1998, all sites will survey for these parasites.

  • Laboratory Survey:  The primary purpose of this survey is to determine whether or not laboratories within the site boundaries are performing cultures for foodborne pathogens. A baseline survey of 230 clinical labs which perform stool cultures in the sites was completed in late 1995. This survey demonstrated that all 230 labs in the five sites routinely culture for Salmonella and Shigella, 95% for Campylobacter, 48% for E. coli O157, 30% for Yersinia, and 19% for Vibrio. The survey was repeated in 1997 to determine the total number of bacterial stool cultures performed, including those that did and did not yield a pathogen, to collect specific information on Campylobacter isolation techniques, and to collect information regarding testing for Cryptosporidium and Cyclospora. Analysis is being conducted by CDC.

  • Physician Survey: The primary purpose of this survey is to determine whether or not physicians who see patients for diarrheal complaints are referring them for laboratory analysis. A total of 5074 surveys were mailed to physicians in non-surgical specialties in five sites in 1996; 2939 (58%) were returned. In 1997, the survey was conducted in Maryland and New York, the two newest sites. Analysis is being conducted by CDC. Stool culturing practices were not influenced by the increased trend of cost containment in medical care.

  • Population Survey:  An outside contractor, Macro International, performs this survey for FoodNet. All residents of the catchment area, including children, are eligible. The primary purpose of this survey is to determine population behavior in the site areas, particularly regarding what foods are consumed and high-risk food consumption and preparation practices. The first full year of data collection was completed in June 1997. A total of 12,209 interviews were conducted. Preliminary analysis at CDC indicates 11% of persons interviewed had a diarrheal illness in the previous 4 weeks, which represents 1.4 diarrheal episodes per person per year. Eight percent of those with a diarrheal illness sought medical care. The second year of data collection began in February 1998.

  • Case-Control Studies: The primary purpose of these studies is to identify patient behavior, food preparation practices, and food consumption preferences which are strongly associated with illness due to one of the specific bacterial pathogens just prior to becoming ill.

    • E. coli O157:H7

      The first year of the E. coli O157:H7 study was completed in May, 1997. Data are being analyzed at CDC and the Minnesota Department of Health. Two hundred cases and 380 age-matched controls were interviewed.

      Preliminary analysis by the Minnesota Department of Health (Heidi Kassenborg) indicates that consumption of pink hamburgers or pink ground beef and visiting a farm are risk factors for sporadic infection from E. coli O157:H7.

    • Salmonella

      The Salmonella serogroups B & D (which includes S. Enteritidis and S Typhimurium DT 104) case-control study began in April 1996 in three sites and in August 1996 in two sites, and ended 12 months later in all sites. Data are being analyzed at CDC. Four hundred eighty-three cases and 916 age-matched controls were interviewed.

    • Campylobacter

      In 1997, it was decided to add a case-control study for Campylobacter which was found to be the most frequent cause of illness in all sites. The questionnaire was developed in 1997 and the study began in January 1998 in four sites, February 1998 in one site, and March 1998 in two sites.

Future Plans

Plan for 1998:

Counties in New York (Genesee, Livingston, Monroe, Ontario, Orleans, Wayne, and Yates) and Maryland (Ann Arundel, Baltimore, Carroll, Harford, Howard, and Baltimore City) will join FoodNet as fully participating sites. An invitation will be presented to all remaining state public health departments in the United States to be considered as the eighth site. Selection of this eighth site will be made in the fall of 1998, and participation will begin in 1999.

Plan for 1999:

The eighth site will begin to participate in FoodNet. Case-control studies for additional pathogens such as Listeria and Cryptosporidium will begin. Additional studies for the Physician survey and Laboratory survey will be performed to validate collected data. The Laboratory survey will be repeated. The FoodNet population under surveillance will increase to 24,979,368 with the addition of statewide surveillance in Georgia and the Albany, NY metropolitan area. The addition of the eighth site will increase the population under surveillance as well.

Foodborne Illness Data

The following information represents findings from the second year of data collection. It is important to note, however, that the tables and charts that follow are based solely on the number of laboratory-confirmed actual cases in the sites.

Population in sites (based on 1996 Census data):


The total United States population is 265,189,612.

These population totals are based on 1996 Census data. Connecticut includes the addition of Fairfield county. Georgia includes the addition of 12 counties.

Active Cases:

There were 8,031 laboratory-confirmed diarrheal cases in 1997 that were attributable to the seven targeted bacterial pathogens (i.e., Campylobacter, E. coli O157:H7, Listeria, Salmonella, Shigella, Vibrio, and Yersinia). This represents an increase of 709 cases (9.6%) over the 7,322 final case figure for 1996. However, the population figure also increased by 1,645,208 (11%). So, a comparison of cases for 1996 and 1997 shows that the rate of cases per 100,000 persons changed from 51.3 to 50.4. (Table 3)

Most frequently isolated pathogen:

For the second year, Campylobacter is the most frequently isolated foodborne bacterium (49.4%); Salmonella is second (27.4%); Shigella is third (15.7%); E. coli O157:H7 is fourth (4.2%); Yersinia is fifth (1.7%); Listeria is sixth (1%); Vibrio is last (0.6%).

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Last Updated On 04/21/1998.