I am Dr. Jeffrey Koplan, Director of the Centers for Disease Control and Prevention
(CDC). I am accompanied by Dr. Stephen Ostroff of the National Center for Infectious
Diseases, which is the organizational component with lead responsibility for food safety
issues at CDC. I would like to thank the Committee for the opportunity to be here today
with my colleagues from the U.S. Department of Agriculture (USDA) and the Food and Drug
Administration (FDA) to describe our Nation's
food safety activities.
Today I will discuss CDC's role in the area
of foodborne diseases and food safety, including how CDC has used resources obtained
through the National Food Safety Initiative to strengthen the Nation's ability to detect and respond to emerging foodborne
disease threats. I will also use examples from surveillance reports and from recent
outbreak investigations to demonstrate how these resources are being applied to today's public health practice.
At its most fundamental level, CDC is the agency that keeps its finger on the pulse of
the Nation's health. CDC is the cornerstone
Federal agency for identifying and monitoring foodborne and other illness and for
documenting the effectiveness of prevention and control efforts, including both voluntary
and regulatory measures. Using this information, we then work to develop ways to improve
disease control and prevention actions. CDC collaborates with partners ranging from State
and local health departments, clinical medicine, academic centers, industry, other
countries, and international organizations. In food safety, CDC works in very close
coordination with the other agencies represented in today's hearing.
Foodborne and waterborne diseases is a target area in CDC's recently released plan, Preventing Emerging
Infectious Diseases: A Strategy for the 21st Century. Public health
priorities in the plan are organized under four broad, interdependent goals, each of which
can be applied specifically to the prevention of foodborne illness: improving surveillance
and response capacity, addressing applied research priorities, repairing the Nation's public health infrastructure and training programs,
and strengthening prevention and control programs required to control emerging,
reemerging, and drug-resistant infectious diseases. Copies of CDC's plan have been provided to the Subcommittee.
CDC's Role in Foodborne Diseases and Food
Safety
CDC plays a critical and unique role as a monitoring, investigative, and advisory
agency that is separate from regulatory agencies, but that works closely with them. CDC
monitors the occurrence of human foodborne disease in the United States
. This includes not
only traditional public health concerns, such as illness caused by pathogens such as Salmonella,
but also newer foodborne threats such as E. coli O157:H7 and Cyclospora
parasites. CDC works with State and local health departments to conduct ongoing
surveillance of cases of foodborne illness and to investigate disease outbreaks, which
often provide the first clue of new or different threats to the food supply. CDC uses both
surveillance data and results of outbreak investigations to identify the factors
responsible for illness so that immediate control measures can be taken and longer term
prevention strategies can be developed. While other agencies measure success of
interventions via reductions in food contamination, CDC's
role in measuring the success of interventions is to see whether they translate into
reductions in the incidence of human cases of foodborne illness. The ultimate test of all
prevention efforts is whether they prevent human illness.
Once an outbreak is detected, the first response is usually from the State or local
health department. Due to limited resources at State and local levels, not all outbreaks
can be adequately investigated and reported. CDC will often be invited by the State health
departments to participate in the investigation if an outbreak is very large or
significant, is thought to involve an unusual pathogen or unexpected food vehicle, affects
multiple states or countries, or when preliminary investigations do not reveal a source.
When investigating an outbreak of a foodborne illness, public health officials must
combine laboratory diagnostic techniques and epidemiologic investigative methods to
determine the causative agent of the illness, the food vehicle responsible for
transmission, and the environmental factors that contributed to the outbreak. If a food is
identified as the source of illness, CDC collaborates with FDA or USDA on the
investigation and control of the outbreak, based upon which agency regulates the suspected
food.
In addition to our surveillance and response activities, CDC also conducts applied
foodborne illness research. Some examples include developing laboratory diagnostic tests
where none currently exist, such as detection of hepatitis A virus in food and detection
of Norwalk-like viruses or Cyclospora in clinical specimens and foods; developing
methods to subtype, or "fingerprint", bacteria, viruses, and parasites causing foodborne
illness; conducting risk factor studies for foodborne illness in special populations, such
as the immunocompromised; and performing cost-effectiveness studies of potential
prevention measures such as routine use of hepatitis A vaccine in food workers.
The public health infrastructure is the underlying foundation that supports the
planning, delivery, and evaluation of public health activities and practices. CDC's ongoing effort to rebuild the U.S. public health
infrastructure that addresses infectious diseases is critical to improve the capacity of
health departments, health care delivery organizations, and clinical and public health
laboratories to detect and report cases of foodborne and other illness and to implement
prevention and control strategies. Part of this effort includes enhancing capacity to
respond to disease outbreaks and training public health professionals to be able to
respond to emerging threats now and in the future.
CDC also engages in educational activities targeted to health care professionals and
the public. Some examples include producing videos on laboratory methods to diagnose
foodborne pathogens and materials on how to avoid foodborne illness among
immunocompromised, high-risk persons. CDC actively participates with FDA, USDA, and other
Federal agencies, industry, and consumer organizations in the Partnership for Food Safety
Education, an ambitious public-private partnership created to reduce the incidence of
foodborne illness by educating Americans about safe food-handling practices through many
activities, including the national Fight BAC!TM Campaign. The purpose of the
Fight BAC!TM Campaign is to help educate consumers about the problem of
foodborne illness and motivate them to take basic sanitation and food-handling steps that
will reduce the risk of foodborne illness.
The Challenges of Food Safety
Although the United States
has one of the safest food supplies in the world, the public
health burden of foodborne diseases is still substantial, and we continue to face
challenges to the safety of our foods. New foodborne pathogens are emerging, old foodborne
pathogens are showing up in new foods, and antimicrobial resistance in foods is
increasing. The eating habits of Americans have changed. We now consume more fresh produce
and seafood and demand a constant supply throughout the year. Changing food habits can
result in a changing pattern of foodborne illness. To meet the demand, an ever increasing
proportion of our food is imported, especially from developing parts of the world. As a
result, we are being exposed to pathogens not commonly found in the United States
, as
demonstrated by the Cyclospora outbreaks associated with raspberries imported from
Guatemala. The array of new products and processing methods, such as pre-packaged salad
mixes, presents another challenge, as does mass production and distribution of foods,
which has the potential to produce diffuse, nationwide illness outbreaks of unprecedented
scale.
New challenges require new, creative ways to do our job more effectively and
efficiently. The President's National Food
Safety Initiative, launched in 1997, recognizes this need and is moving our food safety
system forward. CDC has been an active partner in the development and implementation of
the Food Safety Initiative. Our resources under this initiative have primarily been
targeted to harnessing the information and laboratory technology revolution to propel our
Nation's foodborne disease surveillance system
into the 21st century.
FoodNet
I will provide two examples of CDC's progress
in this area. First is the Foodborne Diseases Active Surveillance Network (FoodNet). The
FoodNet system is a joint effort by CDC, FDA, USDA, and State health departments to
capture a more accurate and complete picture of trends in the occurrence of illness caused
by priority foodborne pathogens. It is built on the foundation of CDC's emerging infectious disease activities, which
provides the basic infrastructure to conduct active disease surveillance. Before 1996, the
Nation's foodborne disease surveillance system
was based on passive reports of illness from clinicians and laboratories which were
submitted to local health departments and then onward to the State health department and
from the State to CDC. Such information lacks timeliness, is often incomplete, and is
highly variable from one place to the next depending on the resources invested at the
state and local level.
FoodNet is part of CDC's Emerging Infections
Programs (EIP's). CDC funds EIP cooperative
agreements with State and local health departments to conduct population-based
surveillance and research that go beyond the routine functions of health departments. In
these sites, the program, which usually involves a partnership between the State health
department and an academic center, canvasses laboratories and other data sources for
illnesses caused by seven different pathogens on an active, ongoing basis using
standardized data collection methods, standard definitions, and standard techniques. Each
case is reviewed and strains are collected and analyzed. Special case-control studies are
conducted across FoodNet sites in order to identify the major risk factors for sporadic
illness, and community surveys are conducted to help determine the overall burden of
foodborne illness, which include mild illnesses which do not come to medical attention or
patients who do not have diagnostic testing performed. Data are electronically submitted
to CDC for collation with rapid turnaround. FoodNet gives high quality data never before
available and also allows determination that any differences across sites are real and not
due to differing surveillance intensity or methodology.
As a demonstration of how rapidly these data can be analyzed and disseminated,
provisional 1998 data was released on March 11, 1999, in CDC's Morbidity and Mortality Weekly Report. The
results are very encouraging. For the five original FoodNet sites which have been
collecting data since 1996, the incidence of Salmonella infections declined 13%
between 1996 and 1998. For Salmonella Enteritidis (SE), the Salmonella subtype
associated with egg contamination which became a major problem in the 1980s, the decline
was especially pronounced. Between 1996 and 1998, the incidence of SE in FoodNet sites
declined by 44%. For Campylobacter, the most common bacterial foodborne pathogen in
the United States
, there was an increase in incidence between 1996 and 1997, but now we
have documented a 15% decline from 1997 to 1998. The incidence of infection with the
parasite Cyclospora decreased to virtually zero after the importation of
raspberries from Guatemala was suspended. These provisional data use 1997 census
estimates. When 1998 census estimates are available later this year, these 1998 rates will
be recalculated and are likely to be slightly lower due to population increases. Although
there may be other explanations for these impressive declines, the fact that they were
seen across sites suggests they are not surveillance artifacts and may be an indication
that prevention measures being implemented by USDA and FDA are working.
PulseNet
A second system to highlight is PulseNet, a system developed in partnership with State
health departments and the Association of Public Health Laboratories. PulseNet is a
network of molecular subtyping (fingerprinting) laboratories at State health departments,
FDA, USDA, and CDC, which enhances the ability of laboratory-based surveillance to rapidly
identify clusters of related foodborne infections of certain pathogens, sometimes
scattered over large geographic areas. This system uses a methodology known as Pulsed
Field Gel Electrophoresis (PFGE) to digest bacterial DNA into fragments which can be run
on gels to produce unique patterns. Like human fingerprints, each bacteria and its
offspring have a unique PFGE pattern. If two bacteria are found with an indistinguishable
pattern, it is likely that they have a common source, meaning they may be part of an
outbreak of many similar cases. CDC has standardized PFGE methodology for E. coli O157:H7
and for Salmonella. Last fall CDC standardized PFGE methodology for Listeria,
not long before there was a multi-state outbreak of listeriosis associated with
contaminated hot dogs. Using funds from CDC's
Epidemiology and Laboratory Capacity (ELC) cooperative agreements and from the Food Safety
Initiative, state health laboratories have obtained PFGE equipment, and CDC has provided
training and standardized methodology to them to test for foodborne pathogens. USDA and
FDA laboratories also participate in the network to allow comparison between animal, food,
and human isolates. By the end of 1999, 33 laboratories will be linked into this network.
Eventually, CDC hopes to include all state laboratories.
To enhance the power of the PulseNet system, in 1998, CDC created a national computer
database of PFGE patterns that is Housed at CDC. Now states can submit PFGE patterns to
the database over the Internet. The computer then automatically scans previously submitted
patterns searching for matches. If a match is found, a signal is given to the submitter
that duplicate patterns are present and where they came from, so that an investigation can
begin to look for a common source. All of this happens in real time, allowing the early
warning system for nascent outbreaks that we all desire.
The impact of PulseNet has been enormous, both in identifying outbreaks that would
otherwise have gone unnoticed, and in allowing us to focus our investigations to determine
the true source and extent of an outbreak. For example in late 1998, an increased number
of cases of listeriosis were noticed. Using PulseNet technology, CDC tested the strains
from several states and determined that many had the same PFGE pattern. Epidemiologic
investigations found a strong association with hot dog consumption in patients with the
outbreak strain, leading to recalls which occurred just before Christmas. Since then, CDC
has continued to work with states to test all available Listeria isolates from
patients since last summer, in order to determine how many cases and deaths occurred as
part of the outbreak and to confirm that the outbreak is over. As of late February, a
total of 97 outbreak-associated cases have been identified in 22 states with 14 fatalities
and 6 still births.
Some of the strains which were tested were different from the outbreak strain. Among
these a second cluster of strains with a common PFGE pattern was found. Investigation of
these cases found they were linked to consumption of a specific imported cheese. Other
small clusters of cases have been identified and are under investigation. If not for the
ability to do the subtyping, these outbreaks never would have been discovered and
investigated, and prevention measures would not have been undertaken.
Another PulseNet example involves Shigella, a bacterial pathogen that can be
foodborne but most often is not. The Minnesota Department of Health, a FoodNet site,
routinely fingerprints its Shigella isolates, and last summer they identified a
cluster of strains with a similar pattern. Epidemiologic investigations found that illness
was linked to eating chopped parsley in two different restaurants. By informing other
states and searching databases for places with an increased number of cases, similar
outbreaks were identified in five other states and Canada. The Shigella from these
outbreaks also had the same PFGE fingerprint. All of the outbreaks were parsley
associated. Working with FDA, the implicated parsley was traced to production fields in
Mexico. Again, if not for routine utilization of PFGE, the links between the outbreaks
would have been missed, the source would not have been identified, and the outbreak would
have spread much further.
PFGE is a powerful tool. It allows us to detect widely dispersed outbreaks and small
clusters that would have previously been missed. This illustrates a central tenet of
epidemiology: better surveillance leads to better and more accurate disease detection,
which in turn leads to more investigations. This causes increased burdens, not only on CDC
and other Federal agencies, but also on state and local partners.
Therefore, as surveillance improves, more outbreaks, not fewer, will be detected.
However, this should not be interpreted as a failure. Rather, it represents success,
because only by finding and investigating the outbreaks can we define risks, develop and
implement interventions, and over the long term target and ultimately eliminate the risk.
National Food Safety Initiative at CDC in FY 2000
CDC is committed to continuing to build a sensitive, timely, and accurate public health
infrastructure for the Nation. To this end, the President's request for CDC for fiscal year 2000 National Food
Safety Initiative is $10,000,000 above the fiscal year 1999 appropriation of $19,476,000.
CDC plans to devote these resources to continue to build the national network of labs
capable of performing PFGE technology and participating in the PulseNet system. We will
increase the number of pathogens monitored in the system in order to detect additional
outbreaks. Other funds will go to expanding the FoodNet system and adding surveillance
components for viral gastroenteritis. In the future, we hope to expand and incorporate
subtyping methods for viral agents and to support the development of subtyping methods for
Cyclospora and Cryptosporidium, parasitic agents for which subtyping is not
sufficiently developed. And finally we will continue to support a system known as DPDx,
which harnesses telemedicine technology to transmit images of parasites under the
microscope to our experts at CDC for appropriate diagnosis. In concert, CDC will continue
to use emerging infections resources to build State health department capacity to conduct
appropriate epidemiologic investigations.
Conclusions
In conclusion, these activities represent a small sample of how CDC supports its state
and local partners and other Federal agencies in monitoring, controlling, and preventing
foodborne illness. Foodborne diseases remain a challenge for public health. To address
this challenge will require continued investments in our public health infrastructure and
strong partnerships among State and local health departments and Federal agencies.
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.
