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Surveillance for Foodborne Disease Outbreaks — United States, 1998–2008

	Surveillance Summaries Volume 62, No. SS-2 June 28, 2013

Surveillance for Foodborne Disease Outbreaks — United States, 1998–2008

Surveillance Summaries

June 28, 2013 / 62(SS02);1-34

L. Hannah Gould, PhD

Kelly A. Walsh, MPH

Antonio R. Vieira, DVM

Karen Herman, MSPH

Ian T. Williams, PhD

Aron J. Hall, DVM

Dana Cole, DVM, PhD

Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases

Corresponding author: L. Hannah Gould, PhD, Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases. Telephone: 404-639-3315; E-mail: lgould@cdc.gov.

Abstract

Problem/Condition: Foodborne diseases cause an estimated 48 million illnesses each year in the United States, including 9.4 million caused by known pathogens. Foodborne disease outbreak surveillance provides valuable insights into the agents and foods that cause illness and the settings in which transmission occurs. CDC maintains a surveillance program for collection and periodic reporting of data on the occurrence and causes of foodborne disease outbreaks in the United States. This surveillance system is the primary source of national data describing the numbers of illnesses, hospitalizations, and deaths; etiologic agents; implicated foods; contributing factors; and settings of food preparation and consumption associated with recognized foodborne disease outbreaks in the United States.
Reporting Period: 1998–2008.
Description of the System: The Foodborne Disease Outbreak Surveillance System collects data on foodborne disease outbreaks, defined as the occurrence of two or more cases of a similar illness resulting from the ingestion of a common food. Public health agencies in all 50 states, the District of Columbia, U.S. territories, and Freely Associated States have primary responsibility for identifying and investigating outbreaks and use a standard form to report outbreaks voluntarily to CDC. During 1998–2008, reporting was made through the electronic Foodborne Outbreak Reporting System (eFORS).
Results: During 1998–2008, CDC received reports of 13,405 foodborne disease outbreaks, which resulted in 273,120 reported cases of illness, 9,109 hospitalizations, and 200 deaths. Of the 7,998 outbreaks with a known etiology, 3,633 (45%) were caused by viruses, 3,613 (45%) were caused by bacteria, 685 (5%) were caused by chemical and toxic agents, and 67 (1%) were caused by parasites. Among the 7,724 (58%) outbreaks with an implicated food or contaminated ingredient reported, 3,264 (42%) could be assigned to one of 17 predefined commodity categories: fish, crustaceans, mollusks, dairy, eggs, beef, game, pork, poultry, grains/beans, oils/sugars, fruits/nuts, fungi, leafy vegetables, root vegetables, sprouts, and vegetables from a vine or stalk. The commodities implicated most commonly were poultry (18.9%; 95% confidence interval [CI] = 17.4–20.3) and fish (18.6%; CI = 17.2–20), followed by beef (11.9%; CI = 10.8–13.1). The pathogen-commodity pairs most commonly responsible for outbreaks were scombroid toxin/histamine and fish (317 outbreaks), ciguatoxin and fish (172 outbreaks), Salmonella and poultry (145 outbreaks), and norovirus and leafy vegetables (141 outbreaks). The pathogen-commodity pairs most commonly responsible for outbreak-related illnesses were norovirus and leafy vegetables (4,011 illnesses), Clostridium perfringens and poultry (3,452 illnesses), Salmonella and vine-stalk vegetables (3,216 illnesses), and Clostridium perfringens and beef (2,963 illnesses). Compared with the first 2 years of the study (1998–1999), the percentage of outbreaks associated with leafy vegetables and dairy increased substantially during 2006–2008, while the percentage of outbreaks associated with eggs decreased.
Interpretation: Outbreak reporting rates and implicated foods varied by state and year, respectively; analysis of surveillance data for this 11-year period provides important information regarding changes in sources of illness over time. A substantial percentage of foodborne disease outbreaks were associated with poultry, fish, and beef, whereas many outbreak-related illnesses were associated with poultry, leafy vegetables, beef, and fruits/nuts. The percentage of outbreaks associated with leafy vegetables and dairy increased during the surveillance period, while the percentage associated with eggs decreased.
Public Health Actions: Outbreak surveillance data highlight the etiologic agents, foods, and settings involved most often in foodborne disease outbreaks and can help to identify food commodities and preparation settings in which interventions might be most effective. Analysis of data collected over several years of surveillance provides a means to assess changes in the food commodities associated most frequently with outbreaks that might occur following improvements in food safety or changes in consumption patterns or food preparation practices. Prevention of foodborne disease depends on targeted interventions at appropriate points from food production to food preparation. Efforts to reduce foodborne illness should focus on the pathogens and food commodities causing the most outbreaks and outbreak-associated illnesses, including beef, poultry, fish, and produce.

Introduction

Surveillance for Foodborne
Disease Outbreaks

Foodborne diseases cause an estimated 48 million illnesses each year in the United States, including 9.4 million caused by known pathogens (1,2). Only a minority of foodborne illnesses, hospitalizations, and deaths occur as part of recognized outbreaks (3). The contaminated food that caused an individual illness rarely is determined. Therefore, foodborne disease outbreak surveillance provides valuable insights into the agents that cause foodborne illness, types of implicated foods and ingredients, and settings in which transmission occurs.
CDC conducts surveillance for foodborne disease outbreaks in the United States through the Foodborne Disease Outbreak Surveillance System. State, local, and territorial public health departments have primary responsibility for identifying and investigating foodborne disease outbreaks caused by enteric bacterial, viral, parasitic, and chemical/toxic agents. At the current system's inception in 1973, paper reports were sent to CDC; in 1998, a revised reporting form was implemented, and the system became web-based. The revised form expanded the range of food information, settings, and contributing factors that could be reported. By 2001, all state, local, and territorial health departments were submitting reports through the web-based version of this form, the electronic Foodborne Outbreak Reporting System (eFORS). Data were collected through eFORS until 2008, when the system transitioned to an enhanced form and reporting platform, the National Outbreak Reporting System (NORS). NORS also collects information on enteric disease outbreaks with modes of transmission other than food, including: person-to-person contact, animal contact, water, and environmental contamination. Information about NORS is available at http://www.cdc.gov/nors. Foodborne disease outbreaks have been a nationally notifiable condition since 2010.
Foodborne disease outbreak surveillance serves multiple purposes:

• Identification of foods. Foodborne disease outbreak investigations have identified common and rare foods associated with foodborne disease outbreaks. Data from outbreaks can help researchers identify changes over time in commonly reported food vehicles, providing insight into the effectiveness of regulations and control measures. These data also help to identify specific pathogen-food pairs repeatedly linked to outbreaks and illnesses.
• Identification of etiologic agents. Outbreak investigations are a key means of identifying new and emerging pathogens and tracking ongoing problems. Prompt and thorough investigations of outbreaks aid in the timely identification of etiologic agents and can lead to appropriate prevention and control measures. Summaries of the results of these investigations provide information on the relative public health importance and impact of specific pathogens.
• Identification of settings. Data from outbreaks provide information regarding the food preparation and consumption settings where outbreaks occur. These data help to identify food preparation and handling practices that can be targeted by interventions to reduce foodborne diseases.
• Identification of points of contamination. The investigation of outbreaks informs prevention and control measures in the food industry by identifying points of contamination where action can be taken to reduce contamination by pathogens. Improvements at multiple points of food production (e.g., farm, slaughterhouse, and production plant) can contribute to reducing contamination in the food supply.
• Describing trends in foodborne disease outbreaks. Summarizing the findings of these investigations illustrates how outbreaks have changed over time and provides information about the efforts needed to prevent them. Data from outbreaks are used to measure progress toward food safety goals to reduce the incidence of illness caused by selected pathogens.

Summaries of data reported to the Foodborne Disease Outbreak Surveillance System have been published previously for 1983–1987 (4), 1988–1992 (5), 1993–1997 (6), 1998–2002 (7), 2006 (8), 2007 (9), and 2008 (10). This report summarizes epidemiologic data on foodborne disease outbreaks reported to CDC during 1998–2008, the eFORS reporting period, including assessments of changes in reporting over time and trends in source attribution. These findings are intended to be used by health departments and regulatory agencies to identify foods and settings for intervention likely to yield the greatest public health benefit.

Methods