Foodborne disease is an important public health problem in the United States, with
an estimated 9.4 million domestically acquired illnesses and 1351 deaths from known
pathogens each year [1]. The Foodborne Diseases Active Surveillance Network (FoodNet)
tracks important foodborne illnesses, generating information that provides a foundation
for food safety policy and prevention efforts. FoodNet has provided information that
contributes to food safety efforts by estimating numbers of foodborne illnesses, monitoring
trends in incidence of specific foodborne illnesses over time, attributing illnesses
to specific foods and settings, and disseminating information [2, 3]. Since it started
in 1996, FoodNet has been an excellent example of partnership among federal and state
agencies (Figure 1). This Clinical Infectious Diseases supplement contains a variety
of articles that provide new information on current issues; together, they highlight
FoodNet’s central role in US surveillance and investigation of foodborne disease.
Figure 1.
Foodborne Disease Active Surveillance Network (FoodNet) sites in 2011, including Connecticut,
Georgia, Maryland, Minnesota, New Mexico, Oregon, Tennessee, and selected counties
in California, Colorado, and New York. FoodNet is a collaborative program among the
Centers for Disease Control and Prevention, 10 participating state health departments,
the US Department of Agriculture’s Food Safety and Inspection Service, and the Food
and Drug Administration.
FoodNet’s core work is ongoing active, population-based surveillance for laboratory-confirmed
infections caused by 9 pathogens transmitted commonly through food, as well as for
hemolytic uremic syndrome. Several articles in this supplement report on these core
data, examining trends and providing regulatory and public health agencies, industry,
and consumer groups with data needed to prioritize and evaluate food safety interventions
and monitor progress toward national health objectives. For example, Ong et al [4]
report the dramatic decline in Yersinia enterocolitica infections since 1996, particularly
among young black children. Not all the news is good, however; Newton et al [5] analyze
data from FoodNet and the Cholera and Other Vibrio Illness Surveillance System (COVIS),
showing that Vibrio infections have increased nationally. Two articles in this supplement
examine FoodNet surveillance data on invasive listeriosis. The article by Silk et
al [6] summarizes trends in surveillance data from 2004 to 2009, whereas Pouillot
et al [7] use FoodNet surveillance data to estimate the relative risk of listeriosis
by age, pregnancy, and ethnicity, providing new insights into variations in risk across
the population. Together, these articles emphasize that to substantially decrease
the incidence of listeriosis, prevention measures should target higher-risk groups,
particularly pregnant women, especially Hispanics, and older adults. Hall et al [8]
examine trends in Cyclospora infection, showing that outbreaks and international travel
play an unusually large role in the epidemiology of these infections and suggesting
that prevention efforts would most effectively focus on foods from and travel to endemic
areas.
FoodNet continuously works to improve the quality of its surveillance data and methods
for analysis. In this supplement, Henao et al [9] describe the methods and rationale
surrounding the introduction, in 2011, of a measure of overall change in the incidence
of infection over time using surveillance data on infections caused by 6 bacterial
pathogens. This measure, which provides a comprehensive picture of changes in incidence
of foodborne infections, documents a 23% decline overall in incidence for these pathogens
in 2010 compared with the first 3 years of surveillance (1996–1998). Although it does
not replace pathogen-specific trend data, this summary measure can help inform the
development and assessment of policies and interventions to prevent foodborne illness.
Another article, by Manikonda et al [10], reports on a study to validate the reporting
of deaths in FoodNet surveillance, an important issue because deaths, although rare,
are disproportionately responsible for the economic and human costs of foodborne disease.
Finally, Ong et al [11] examine the impact of case ascertainment strategies and case
definitions on surveillance for pediatric hemolytic uremic syndrome in FoodNet.
Several articles in the supplement elucidate aspects of the “surveillance steps” that
are necessary for a case of infection to be ascertained by FoodNet surveillance. FoodNet
and many other surveillance systems for bacterial enteric infections are based on
culture-confirmed infections, so FoodNet surveillance data must be interpreted in
the context of the “surveillance steps” that lead to culture confirmation: the ill
person must seek medical care, a stool specimen must be submitted, and the clinical
laboratory must test for and identify the pathogen. In particular, the recent and
ongoing shift among clinical laboratories toward culture-independent methods for detecting
enteric pathogens is of great importance. Three articles in this supplement explore
this issue. Cronquist et al [12] summarize the challenges and opportunities that culture-independent
tests present for surveillance. To ensure that surveillance remains robust, the authors
emphasize the need for public health practitioners to clearly explain the value of
surveillance for enteric pathogens, its crucial role in outbreak detection and tracking
trends, the role of outbreak detection and robust trend data in protecting public
health, and the need to collaborate with all stakeholders to develop solutions. Campylobacter
is one of the pathogens for which culture-independent testing methods have been introduced.
In their article, Hurd et al [13] provide baseline information for understanding changing
laboratory practices by documenting the procedures used by clinical diagnostic laboratories
for Campylobacter detection in FoodNet in 2005, including the use of culture-independent
methods and adherence to guidelines for culture-based tests. The increased availability
and use of tests that detect Shiga toxin in stool specimens is one reason why the
number of reported non-O157 Shiga toxin–producing Escherichia coli infections in FoodNet
is increasing, although Clogher et al [14] report that physician ordering and interpretation
of Shiga toxin test results remain suboptimal.
FoodNet also monitors the “surveillance steps” related to medical care by collecting
information from the general population through periodic FoodNet population surveys.
These surveys provide essential information for estimating the numbers of persons
with diarrheal illness, the severity of illness, and the frequency with which persons
seek medical care and submit a stool sample for that illness. These surveys also collect
information on consumption of foods, including “risky” foods that are frequently linked
to foodborne illnesses. Shiferaw et al [15] use data from the most recent FoodNet
population survey, conducted in 2006–2007, to explore sex differences in food consumption,
showing intriguing patterns of similarity and difference that may be useful not only
in educational efforts but also in generating hypotheses about possible food sources
for outbreaks.
FoodNet surveillance data can be compared with data from other surveillance systems,
from surveys, and from special studies to enhance our understanding of disease burden
and trends. Linking data between surveillance systems can increase FoodNet’s utility,
as exemplified by the article by Shiferaw et al [16], who combined FoodNet data on
Shigella infections with data from the Centers for Disease Control and Prevention
(CDC) National Antimicrobial Resistance Monitoring System (NARMS). Ailes et al [17]
also use data from FoodNet population surveys, along with data from FoodNet case-control
studies, to explore the roles of medical care seeking, medical practices, and risk
factors in geographic variation in the rates of culture-confirmed Campylobacter infection.
These differences did not fully explain the geographic variation in campylobacteriosis,
suggesting that real and substantial differences in risk may exist within the United
States.
The attribution of enteric infections to exposure sources starts with understanding
the roles of various transmission routes. Not all enteric infections are transmitted
through food, and not all that are transmitted through food are acquired domestically.
In this supplement, Hale et al [18] adapt the methods developed in FoodNet to estimate
the total US numbers of illnesses [1] to estimate the annual numbers of illnesses
caused by 7 enteric pathogens that can be attributed to contact with animals and their
environments. They estimate that this transmission route is responsible for about
13% of these illnesses. FoodNet has collected information on international travel
history since 2004. Kendall et al [19] describe these data, reporting that about 13%
of FoodNet cases are associated with international travel, primarily in travelers
returning from Latin America and the Caribbean, although travel to Africa carries
the greatest risk. For those infections that are transmitted through food, sound information
on food source attribution is essential to develop and prioritize food safety interventions.
In an analysis that not only explores trends in Salmonella serotype Enteritidis infection
in FoodNet data but also considers these trends in light of data on processed broiler
chickens, Chai et al [20] bring our attention to a recent increase in human serotype
Enteritidis infections, highlighting the importance of eating chicken as a risk factor.
FoodNet has been able to make a unique contribution to food source attribution by
using its surveillance platform to conduct case-control studies to assess risk factors
for sporadic (ie, not outbreak-associated) infections. However, many approaches to
food source attribution rely on data from outbreak investigations in which the etiologic
agent and the food vehicle are identified. Successful investigation—that is, identification
of the agent and vehicle—of a high proportion of foodborne outbreaks is essential
to this work. Murphree et al [21] demonstrate the importance of collecting fecal specimens
and conducting analytic epidemiologic studies as important determinants of success
in outbreak investigations.
In 2011, the CDC released new estimates of the number of foodborne illnesses in the
United States, the Food Safety Modernization Act was signed into law, and new national
health objectives for foodborne illness were set as part of the Healthy People 2020
goals. All of these initiatives, as well as continued concern about food safety on
the part of the public and policy makers, emphasize the need for precise and accurate
information about foodborne disease. Regulators and other public health officials,
consumer advocates, industry, and others need information on trends, high-risk populations,
and the foods causing illness so that interventions can be targeted most efficiently
and effectively. FoodNet provides the articles in this supplement as part of its efforts
to disseminate the results of its surveillance and analytic work. Although FoodNet
surveillance is conducted in a geographic area that covers only 15% of the US population,
the data it generates are a valuable resource for the entire United States. The FoodNet
program shows the impact that high-quality, nationally coordinated surveillance can
have on public health and policy.