Good morning. I am Dr. David Satcher, Director of the
Centers for Disease Control and Prevention (CDC). I am
accompanied by Dr. Morris Potter with CDC's National Center for
Infectious Diseases. We are pleased to be here this morning to
discuss CDC's programs to monitor, prevent, and control foodborne
diseases in the United States.
The public health burden of foodborne diseases in the United
States is substantial. Each year we estimate that millions of
persons become ill and thousands die from foodborne diseases.
The cost of these illnesses to the U.S. economy is several
billion dollars a year. Many different pathogens and toxins have
been described as causes of foodborne disease and new ones
continue to be identified. Although I will be addressing
infectious foodborne diseases, natural and environmental toxins
may sometimes also be present in our foods. Foodborne diseases
are common and, in principle, preventable. Many foodborne
problems that were formerly important are now well controlled by
standard prevention strategies, such as pasteurizing raw milk,
appropriately managing the canning of food, and ensuring that
restaurants and other food preparation areas are clean and well
maintained. However, new challenges continue to arise, and new
efforts are required to understand, prevent and control them.
Preventing foodborne disease requires a coordinated program
of risk assessment and risk management involving Federal, State,
and local agencies. CDC's primary role in this coordinated effort
is that of characterizing the risk of foodborne disease.
In a 1992 report, Emerging Infections: Microbial Threats to
Health in the United States, the Institute of Medicine (IOM)
stated: "The potential for foods to be involved in the emergence
or reemergence of microbial threats to health is high, in large
part because there are many points at which food safety can be
compressed." This IOM report underscored the ongoing threat from
emerging infectious diseases and stressed that increased
vigilance and enhanced response capacity are needed to overcome
years of complacency. The report provided specific
recommendations for action by CDC and other federal and state
agencies and emphasized a critical leadership role for CDC in a
national and global effort to monitor, prevent, and control
emerging infectious diseases.
CDC took the recommendations in the IOM report very
seriously. In 1994, after extensive consultation and input from
numerous outside organizations and experts, CDC released a plan,
"Addressing Emerging Infectious Disease Threats: A Prevention
Strategy for the United States." This plan addresses necessary
action for revitalizing our Nation's ability to identify,
contain, and prevent illness from emerging and reemerging
infectious diseases. Particularly critical to meeting the
challenge are CDC's partnerships with both domestic and
international organizations. With the $18.4 million provided by
Congress, CDC has begun implementation of some of the highest
priority steps in this plan.
Many aspects of CDC's plan deal with emerging infectious
foodborne diseases and complement with sections of the Food and
Drug Administration's (FDA) 1995 Food Code, and the mandatory
HACCP-based food safety program being designed and implemented by
FDA and the U.S. Department of Agriculture (USDA).
Beginning in December 1994 and during 1995, I chaired an
Interagency Working Group, established under the aegis of the
Committee on International Science, Engineering, and Technology
Policy (CISET) of the President's National Science and Technology
Council. This working group, representing almost 20 agencies,
reviewed the global threat of infectious diseases. The report of
the CISET working group cites CDC's role as the lead U.S. agency
in domestic disease surveillance, prevention and control, and
emphasizes that surveillance and response capacity must be
enhanced. It also emphasizes that we need the capacity to assist
other countries and the World Health Organization in
investigation and control of outbreaks that may affect the health
of our Nation.
I have provided copies of CDC's plan and the CISET working
group report to members of the committee.
To monitor, prevent, and control foodborne diseases, CDC has
developed and used a number of strategies. Today, I will review
several of these strategies. In my testimony I will provide: (1)
an overview of CDC's foodborne disease surveillance systems, and
(2) an overview of the public health impact of anti-microbial
resistance in the pathogens that cause foodborne disease and
CDC's monitoring system for this problem. Additionally, I will
give an example of CDC's approaches to an emerging foodborne
pathogen, E. coli 0157:H7, and to a reemerging foodborne
pathogen, Salmonella serotype Enteritidis.
FOODBORNE DISEASE
SURVEILLANCE SYSTEMS
When a person becomes ill with a foodborne disease, he or she
may be part of an outbreak -- a cluster of patients who all have
the same illness after consuming the same food -- or may have a
sporadic illness -- an illness that is not part of a recognized
outbreak. Investigations of outbreaks can rapidly determine the
source and nature of the illness and identify the control
measures needed. However, most persons have sporadic illnesses
and these sporadic illnesses often are not diagnosed or
identified as being caused by food. Even if they are recognized
as being foodborne, it is usually not possible, for single cases,
to determine which food is the source of the infection. Since
sporadic cases are far more common than outbreaks, they are a
prime target for prevention efforts.
Effective public health surveillance is key to identifying
and monitoring the prevalence of foodborne disease. CDC, in
collaboration with State and local health departments, conducts
surveillance for foodborne diseases in several different ways.
The goals of surveillance are to estimate the magnitude of the
problems posed by specific foodborne pathogens, to monitor
changes over time in order to guide prevention efforts, and to
detect outbreaks so that emergency actions can be taken,. CDC
uses four principal surveillance systems to obtain information on
diseases caused by foodborne pathogens.
Physician-based Surveillance
One system we use to obtain information is physician-based
surveillance. In this system, physicians report specific disease
entities case-by-case to local health departments.
Physician-based surveillance is relatively fast but, because it
depends on clinical assessments, it may not always be completely
accurate. It is also relatively incomplete, since it requires
that patients seek medical care, and that physicians recognize
the foodborne nature of the illness, request the appropriate
tests, and notify local health authorities. Despite these
limitations, it is a good system for public health emergencies
requiring rapid response. For example, CDC maintains
physician-based surveillance for botulism. The occurrence of
this disease is a public health emergency because of the severity
of the illness and the likelihood that one case may herald an
outbreak. CDC encourages physicians who suspect they may have a
patient with botulism to report it to the state health department
authorities immediately. CDC maintains a 24-hour emergency
consultation service to discuss suspect cases of botulism and to
provide emergency diagnosis and treatment, including emergency
provision of a limited supply of botulism antitoxin.
Clinical Laboratory-based Surveillance
A second way CDC obtains information is from clinical
laboratories. This method depends on a laboratory diagnosis of a
specific infection and notification of public health authorities.
For some infections, the pathogen will then be referred to the
state public health laboratory for more detailed identification.
Laboratory-based surveillance information is more accurate than
physician-based surveillance because the infection is
definitively diagnosed- however, this system is somewhat slower
than physician- based surveillance. Neither physician-based nor
laboratory-based surveillance detects illness in persons who do
not seek medical care. Laboratory-based surveillance also will
not detect illness in those patients for whom the pathogen that
caused the illness is not determined. As an example of
laboratory-based surveillance, CDC tracks Salmonella infection in
the United States. Each year about 40,000 culture-confirmed
cases of human infection are reported. Public health
laboratories in each state further characterize these Salmonella
isolates by dividing them into different subtypes. Information
from the laboratories is transmitted electronically to CDC by the
Public Health Laboratory Information System (PBLIS) which is a
PC-based software application developed by CDC in cooperation
with the Association of State and Territorial Public Health
Laboratory Directors. This surveillance system can detect
outbreaks of a particular type of Salmonella even if it occurs in
a number of states. Some isolates are submitted to CDC's
reference diagnostic laboratories for further characterization.
Outbreak Investigations
A third source of surveillance data we use to track foodborne
diseases is information gathered during outbreak investigations
conducted by local and State health departments and, when
requested, by providing CDC assistance to these health
departments. Due to limited resources at the State and local
levels, only a small fraction of outbreaks are actually
recognized, investigated, and have the results reported .
Approximately 400-500 outbreaks are reported to CDC each year,
accounting for 10,000 to 12,000 persons with foodborne illness.
The outbreaks that are investigated tend to be the most dramatic.
The outbreak investigation surveillance system is useful for
providing detailed information on particular diseases and on the
type and severity of outbreaks that occur in various locations,
for example, in nursing homes. Outbreak investigations are often
critical in identifying contaminated foods that can then be
removed from the marketplace, and in elucidating the problems in
food production that lead to foods being contaminated with
disease-causing organisms.
Active Foodborne Disease Surveillance
A fourth source of data is CDC's recently developed active
foodborne disease surveillance system. With funding provided by
Congress in FY 1995 and 1996 to begin implementation of CDC's
plan for emerging infectious diseases, including foodborne
diseases, we have begun to address the highest priorities of the
plan. Included in these priorities are cooperative agreement
funding to 15 state and local health agencies to strengthen
surveillance and response capacity for infectious diseases, such
as infections caused by E. coli 0157:H7. Emerging Infections
Programs (EIP) have also been established in four health
departments (California, Connecticut, Minnesota, and Oregon), in
partnership with universities and other organizations and
agencies, to address key questions regarding foodborne and other
illnesses nationally, as well as issues related to infectious
diseases of special concern to their own state.
CDC's active foodborne disease surveillance system is
conducted in CDC's four Emerging Infections Program sites and in
metropolitan Atlanta. The FDA and USDA's Food Safety and
Inspection Service (FSIS) are providing financial assistance and
are collaborating with CDC in this system. These five sites
represent about 5% of the U.S. population. At these sites, we
actively seek out information on foodborne illnesses identified
by clinical laboratories and collect information from patients
about their illnesses. We then conduct investigations to
determine the foods linked to specific pathogens. As data are
collected, this surveillance system will provide important
information about changes over time in the burden of foodborne
diseases and will help the agencies evaluate current food safety
initiatives and develop future food safety activities.
Initial data from this surveillance system have already
identified an outbreak of Yersinia enterocolitica infections
among infants in Atlanta and an outbreak of Salmonella infections
in Oregon traced to alfalfa sprouts. This surveillance system
has also confirmed that Campylobacter is the most frequently
isolated foodborne bacterium from persons with diarrhea.
Recognizing the high incidence of Campylobacter infections, with
the potential for complications such as Guillain-Barre syndrome,
CDC investigators anticipate conducting a case-control study in
1997 to pinpoint the major foods and other risk factors
responsible for Campylobacter infections. This information will
be important in designing and implementing prevention strategies.
The EIP sites can provide a framework for conducting
surveillance for many other infectious diseases as well as
physician-diagnosed syndromes such as hemolytic uremic syndrome
(HUS). The President has requested an additional $26 million for
FY 1997 for further implementation of the CDC plan. Included in
our plans with additional funding, is the establishment of three
additional Emerging Infections Programs and support to 10-15
additional State and local health departments to strengthen their
surveillance and response capacity.
ANTI-MICROBIAL RESISTANCE AND FOODBORNE PATHOGENS
We are also using the Emerging Infections Program sites to
actively monitor for the increasing problem of
antibiotic-resistant foodborne pathogens. Bacteria become
resistant to antibiotics as a consequence of antibiotic use in
humans and animals. Antibiotics used in humans can lead to
resistant bacteria that can be spread in communities. For
example, we are seeing significant increases in resistant
pneumococcus (a cause of pneumonia), gonococcus (the cause of
gonorrhea), and Mycohacterium tuberculosis (the cause of
tuberculosis). In addition, many pathogens that are spread among
patients in hospitals are highly resistant, and these antibiotic-
resistant infections can be life-threatening and untreatable with
currently available antibiotics.
The use of antibiotics in animals similarly leads to
resistant bacteria in animals. Bacteria from healthy animals can
contaminate food and cause human illness. When the bacteria from
animals are resistant to antibiotics, the resulting human
infection may be more difficult to treat. There is a clear
relationship between the use of antibiotics in animals and the
appearance of resistant human infections. For example, most
human Salmonella infections can be traced to foods of animal
origin, and CDC's periodic surveys have documented an increase in
antibiotic resistance of Salmonella strains isolated from humans
from 16% of strains in 1979 to 31% in 1990. Although most
persons with Salmonella infection recover without antibiotic
treatment, antibiotics can be life-saving in severe infections
which spread to the bloodstream.
One particular class of antibiotics, fluoroquinolones, has
been particularly important in the treatment of severe infections
of humans. Resistance to fluoroquinolones has emerged in some
human pathogens. One fluoroquinolone was recently approved by
FDA for use in food animals. Slowing the emergence of resistance
depends on prudent use of antibiotics in both humans and animals.
Approval of this fluoroquinolone was restricted to specific uses
as a prescription product in one species, and use for other
purposes and in other animals is discouraged by FDA.
In early 1996, because of concern about the possibility of
emergence of resistance, CDC began collaborating with FDA on a
surveillance system for antibiotic resistance in Salmonella
strains isolated from humans. In parallel with this surveillance
of human strains, USDA, also in collaboration with FDA, is
monitoring for occurrence of resistant Salmonella strains
isolated from animals, meat, poultry, and eggs. This
collaborative effort, designed specifically to detect the
emergence of antibiotic resistance in foodborne pathogens, is an
important component of our efforts to improve surveillance for
new and emerging pathogens.
EMERGING FOODBORNE PATHOGEN - E. COLI 0157:H7
In the last 15 years, several bacteria not previously
recognized as foodborne pathogens have become important public
health concerns. These include E. coli 0157:H7, Campylobacter
jejuni, and Listeria monocytogenes. The example of E. coli
0157:H7 can be used to illustrate how CDC and the public health
community monitor, detect and control emerging foodborne
pathogens.
E. coli 0157:H7 was first recognized as a cause of human
illness in 1982 during an investigation by state health
departments and CDC of outbreaks in two states of bloody diarrhea
associated with eating hamburgers from fast-food restaurants. We
now know that about 5% of E. coli 0157:H7 infections are
complicated by renal failure, hemolytic uremic syndrome (HUS).
HUS can lead to stroke and death and is the most common cause of
acute kidney failure in children in the United States. These
first outbreaks of E. coli 0157:H7 represented our initial
recognition of an emerging foodborne pathogen -- that is,
describing the disease and developing public health strategies
for the prevention and control of the new microbial pathogen.
CDC laboratories developed easy methods for identifying E. coli
0157:H7 that could be used by clinical laboratories. Over the
next 10 years, CDC's investigations of outbreaks answered a
number of additional questions. We defined the foods that
typically cause the outbreaks, identified cattle as the usual
reservoir of illness, and demonstrated that either beef or raw
milk produced from healthy cattle could be contaminated by this
serious pathogen. The emergence of E. coli 0157:H7 is associated
with severe disease and the organism is present in healthy cattle
herds.
In 1993, the largest outbreak of E. coli 0157:H7 infections
in the United States occurred in California, Idaho, Nevada, and
Washington. This outbreak was caused by hamburgers served at
many restaurants of one fast-food chain. Over 700 persons became
ill, 195 were hospitalized, 55 developed hemolytic uremic
syndrome (HUS), and 4 children died. Rapid action by CDC, USDA,
and State health departments resulted in recall of the
contaminated hamburgers, and an estimated 800 more cases were
prevented. Following this outbreak, CDC intensified efforts to
improve recognition of E. coli 0157:H7 infections. We produced a
videotape on the laboratory diagnosis of E. coli 0157:H7
infections to encourage clinical laboratories to begin screening
for this bacteria in stool specimens. CDC also worked with the
Council of State and Territorial Epidemiologists to encourage
states to make this infection reportable. As a result of these
enhanced surveillance efforts, the number of illnesses and
outbreaks recognized as due to E. coli 0157:H7 each year since
have markedly increased. Earlier this year, CDC worked with the
Association of State and Territorial Public Health Laboratory
Directors to train personnel from 14 state health departments in
DNA fingerprinting of this organism. DNA fingerprinting has been
a valuable too in investigating foodborne outbreaks and
determining the source of foodborne bacterial contamination.
E. coli 0157:H7 is the most frequently recognized member of a
family of E. coli bacteria. Organisms in this fancily cause
similar diseases around the world. These other E. coli varieties
are more difficult to detect and may be an important cause of HUS
in the United States. In fact, cases of HUS can be a marker for
the presence of these bacteria in the community, and surveillance
for HUS can be an important way of tracking the presence of these
E. coli in the food we eat. CDC is planning to begin national
surveillance for HUS this year in collaboration with the newly
established Emerging Infections Programs and other participants.
This surveillance will provide early warning of other E. coli
bacteria which may be as important as E. coli 0157:H7 in the
future.
REEMERGING FOODBORNE PATHOGEN - SALMONELLA
Foodborne Salmonella infections emerged as a public health
problem in this country in the 1940s and since then have been
routinely reported by physicians to health departments in many
states. Of the more than 2000 different serotypes of Salmonella,
one particular type, Salmonella serotype Enteritidis (SE), is now
a rapidly increasing cause of infection in the United States and
other countries. Examination of the recent SE problem associated
with shell eggs offers insight into the public health
consequences of reemerging foodborne diseases. In the 1970s, SE
represented just 5% of all Salmonella in the U.S. This proportion
had increased to 26% by 1994, which probably represented between
200,000 and 1,000,000 actual infections. The number of
infections began to increase in the northeastern United States as
early as 1979, in the Mid-Atlantic states around 1984, and in the
Pacific region just within the past year.
CDC determined that there was a link between the increase in
human SE infection and contamination of shell eggs. In 1986,
CDC, several State health departments, and the FDA investigated a
large outbreak of SE infections associated with a commercial
stuffed pasta product. Cases were identified in at least 7
states and 3300 people were infected. The pasta was made with a
stuffing that included raw eggs. The eggs used in the stuffing
mix were traced to several farms in the Northeast and SE was
isolated on those farms. Since then, over 500 outbreaks of SE
infections have been reported to CDC, A specific food vehicle was
identified in half of these investigations, and grade A shell
eggs accounted for 80% of those outbreaks for which a vehicle was
determined. The unusual feature of this problem is that Grade A
inspected shell eggs are the source. CDC proposed that the eggs
were contaminated internally in the hen before the shell was
formed, and this hypothesis has since been amply confirmed by
experimental investigations in hens and has led to a
collaboration among CDC, State health departments, FDA, USDA, and
industry to limit the spread of infections among chickens and to
protect consumers who are at high risk.
Eggs can be pasteurized, and the use of pasteurized eggs,
particularly in high-risk settings, such as nursing homes and
hospitals, has been an important public health prevention
recommendation since 1987. CDC worked with FDA to produce a
training video for food service workers in high risk settings
addressing these problems. Investigations by USDA to determine
how chickens become infected have demonstrated that mice are an
important reservoir of SE. The mice on farms transfer SE from one
flock of chickens to another. In Pennsylvania, an aggressive
program of Salmonella control in egg flocks included rodent
control, verification that hens were not infected, and
pasteurizing eggs if infection were detected. A general decrease
in SE infection in the Northeast has been noted. The spread of
SE out of the Northeast, and the recent appearance of SE further
west confirms that larger scale nationwide prevention measures
are needed.
CONCLUSIONS
New foodborne pathogens like E. coli will continue to be
identified, and other known but rare foodborne pathogens like SE
may reemerge as important public health problems. Infections may
arise from changes in the microbes, changes in the industrial
technology that underlies food production and processing, changes
in our choices concerning the foods that we eat, how they are
prepared, and where we eat them, and changes in the demographics
of the U.S. population. The increasing number of elderly and
chronically ill are at particular risk for severe illness caused
by foodborne pathogens.
While research will continue to identify new causes of
foodborne infections that are currently unrecognized, improved
surveillance can measure the impact of these infections and help
to define better means of preventing them. Prevention of
foodborne disease will continue to bridge many disciplines and
agencies, because there are many points of control between the
farm and the consumer. At CDC, the response to the continuing
challenge of foodborne disease includes enhancing scientific
outbreak investigations by applying sophisticated epidemiologic
and microbiologic techniques to field investigations and using
these techniques to trace the source of contaminating
microorganisms. We are improving surveillance efforts by
continuing to improve CDC's electronic transmission system, the
Public Health Laboratory Information System in State health
departments, as well as by adding automated reporting and
outbreak detection analysis. Collaborative active surveillance
systems for foodborne disease will help determine the magnitude
of these diseases and address questions that cannot be answered
by routine surveillance.
Collaborative efforts to educate food preparers and inform
consumers of choices will be key to our prevention strategy.
History tells us that infectious diseases will remain
important evolving, complex public health problems. To meet
these challenges, we must strengthen our capacity to address the
threat of emerging infectious diseases. Investments in
surveillance and response, laboratory research and training, and
epidemiologic investigations will ensure that we are better
prepared to respond and lessen the impact of infectious disease
threats.
Thank you for the opportunity to discuss the surveillance of
foodborne disease. We will be happy to answer questions you or
other members of the subcommittee may have.
