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Testimony on Foodborne Diseases in the U.S. by David Satcher, M.D., Ph.D.
Director, Centers for Disease Control and Prevention Public Health Service
U.S. Department of Health and Human Services

Before the House Committee on Government Reform and Oversight, Subcommittee on Human Resources and Intergovernmental Relations
May 23, 1996


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.


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