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Testimony on The Safety of Food Imports by Stephen M. Ostroff, M.D.
Associate Director for Epidemiologic Science
National Center for Infectious Diseases
Centers for Disease Control and Prevention
U.S. Department of Health and Human Services

Before the Senate Committee on Governmental Affairs, Permanent Subcommittee on Investigations
July 9, 1998

Good morning. I am Dr. Stephen M. Ostroff, Associate Director for Epidemiologic Science at the National Center for Infectious Diseases, Centers for Disease Control and Prevention (CDC). I am accompanied by Dr. Barbara Herwaldt, also of the National Center for Infectious Diseases. I am pleased to be here this morning to discuss CDC's programs to monitor, prevent, and control foodborne diseases in the United States. I will provide an overview of CDC's foodborne disease surveillance systems and describe cyclosporiasis associated with imported raspberries as an example of our role in outbreak response.

Although the United States has one of the safest food supplies in the world, the public health burden of foodborne diseases is still substantial. The Council for Agricultural Science and Technology has estimated that as many as 9,000 deaths and 6.5 to 33 million illnesses in the United States each year are fool-related. Foodborne disease costs the U.S. economy several billion dollars annually. A variety of pathogens and toxins have been described as causes of foodborne disease, and new ones continue to be identified.

In 1997, in response to the growing concern about food safety, the President announced the National Food Safety Initiative. CDC's collaborative involvement with the Food and Drug Administration (FDA), the U.S. Department of Agriculture (USDA), and the Environmental Protection Agency in the ongoing expansion of this initiative responds to the new challenges by building a national early warning system for hazards in the food supply through enhanced capacity for surveillance and outbreak investigations at the State and federal levels. Specific activities of the Initiative include expanding the scope of FoodNet, CDC's active foodborne disease surveillance system, using it to define the true incidence of many diagnosed foodborne infections and to assess their sources and potential for control; developing and standardizing new and rapid diagnostic techniques and molecular subtyping, or fingerprinting, for foodborne pathogens; and designing and delivering training programs for epidemiologists, laboratorians, and health professionals.

Foodborne diseases are common and, in principle, preventable. Some of the causes of foodborne diseases that were formerly problematic 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, including the increasing globalization of our food supply, larger scale production and distribution networks, and changing dietary habits; and new efforts are required to address these issues.

Preventing foodborne disease requires a coordinated program of risk assessment and risk management involving Federal, State, and local agencies and non-governmental partners. CDC's primary role in this coordinated effort is to identify foodborne hazards, characterize the risk of foodborne disease, and identify strategies that will prevent additional cases. In 1994, CDC issued a strategic plan, Addressing Emerging Infectious Disease Threats: A Prevention Strategy for the United States, which emphasized surveillance, applied research, and prevention activities. An updated version of this plan will be published later this year. As in the 1994 plan, many aspects of the new version of the plan deal with emerging infectious foodborne diseases. The plan complements sections of FDA's 1997 Food Code and the Hazard Analysis and Critical Control Point (HACCP) food safety programs being implemented by FDA and USDA's Food Safety and Inspection Service (FSIS) and provides a platform from which CDC's role in the National Food Safety Initiative, which was launched in 1997, can be instituted. Iden

tification of Foodborne Diseases Problems

A person who becomes ill with a foodborne disease may be part of an outbreak or cluster (a group of patients who all have the same illness after consuming the same food) or may have a sporadic illness (an illness that may be an isolated occurrence and not part of a recognized cluster). Usually, investigations of outbreaks can rapidly determine the source and nature of the illness and identify the control measures needed to prevent additional cases. However, sporadic illnesses are often not diagnosed or considered to be foodborne. Even if they are recognized as being foodborne, it is usually impossible, for single cases, to determine which food is the source of the infection. Because individual 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 is typically notified of a potential foodborne disease problem by a State or local health department or by an astute clinician or laboratorian who notices an unusually large number of cases of a certain disease. Physician-based surveillance is useful for public health emergencies that require rapid response, such as potentially lethal botulism, where one case could herald an outbreak and immediate public health action is necessary. Clinical laboratories help detect foodborne diseases by tracking the number of times they identify a specific pathogen. Clinical laboratory-based surveillance has identified multiple outbreaks, including a recent multistate outbreak of Salmonella Agona infection linked to cereal. State public health laboratories play an important role in further characterizing the strains isolated from ill people, to see whether there are groups of similar pathogens. Taking advantage of recent advances in computer technology and molecular biology, CDC has developed PulseNet, 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.

Another source of data is CDC's FoodNet, which is conducted in CDC's seven Emerging Infections Program sites developed as part of the 1994 emerging infections plan. The FDA and the Food Safety and Inspection Service (FSIS) of USDA are providing financial assistance and are important collaborators with CDC in this system. The seven active surveillance sites cover about 7.7% of the U.S. population. These sites actively seek out information on foodborne illnesses identified by clinical laboratories, collect information from patients about their illnesses, and conduct investigations to determine which foods are linked to specific pathogens. As data are collected, this surveillance system provides 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.

For these surveillance systems to be effective and for an illness to be identified as caused by a foodborne pathogen, several things must occur. A person who eats contaminated food and becomes ill must seek medical attention or contact the health department. The patient's clinicians must obtain appropriate diagnostic tests. The laboratory results must be reported to the health department. Information must be assessed to recognize a potential outbreak. Often, not all of these steps occur, and sporadic illnesses and outbreaks are not recognized or reported.

Outbreak Investigations

Once an outbreak is detected, the first response is usually from the State or local health department. When necessary, the State or local health department conducts an outbreak investigation. Due to limited resources at State and local levels, not all outbreaks can be investigated and reported. 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, CDC will often be invited by the State health departments to participate in the investigation.

When investigating an outbreak of a foodborne illness, public health officials must combine laboratory diagnostic techniques and epidemiologic investigative methods to determine both the causative agent of the illness and the vehicle for its transmission. This involves interviews with patients and comparison of their responses to those of non-ill persons (control subjects) to determine which foods are implicated. 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 food suspected.

Approximately 400-500 foodborne outbreaks are reported by State health departments to CDC each year, accounting for 10,000 to 12,000 persons with foodborne illness. CDC summarizes the information in these reports through its Foodborne Disease Outbreak Surveillance System. The reports provide useful, detailed information on particular diseases and on the type and severity of outbreaks that occur in various settings, such as nursing homes or schools. Outbreak investigations can lead to effective prevention strategies, as they 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 disease.

Case Study: Cyclospora cayetanensis

CDC's role in outbreak investigation is well illustrated by the 1996 and 1997 outbreaks of infection caused by Cyclospora cayetanensis, a recently characterized parasite that causes a gastrointestinal illness called cyclosporiasis. This illness is typically characterized by watery diarrhea and other symptoms, such as nausea, abdominal cramps, weight loss, and fatigue. If not treated, the illness can be severe and prolonged. Before 1996, most of the small number of cases of cyclosporiasis in the United States occurred in travelers who had been in developing countries, and only three small U.S. outbreaks had been reported.

When the pattern of Cyclospora infections changed in 1996 and health departments noted cases of cyclosporiasis in people who had not traveled overseas, CDC was notified promptly. In mid-May of 1996, health departments in Florida and New York informed CDC that sporadic cases of cyclosporiasis had been identified in their states. At the end of May, health departments in Texas and Canada informed CDC that some people who had attended specific events, such as a party, had become ill with cyclosporiasis. Thus, CDC was notified of "clusters" of cases, which indicated that an outbreak might be occurring. In June, CDC learned of additional sporadic cases and clusters in the eastern United States and Canada.

Ultimately, 55 clusters with a total of 725 cases of cyclosporiasis were reported to CDC by 14 States, the District of Columbia, and two Canadian provinces. The 55 clusters were associated with events that occurred May 3 through June 14, 1996. In addition, 740 sporadic cases that were not associated with identified events or overseas travel were reported, for an overall total of 1,465 cases from 20 States, the District of Columbia, and two provinces. Twenty-two people are known to have been hospitalized, but no deaths are known to have occurred. Because in most foodborne outbreaks, particularly those that involve more than one locality, many affected cases are unrecognized or unreported, the total number of cases of cyclosporiasis that occurred in this outbreak may have been much larger than the officially reported number.

CDC played many roles in the outbreak investigation, including serving as the national reference laboratory for identifying Cyclospora in stool specimens and thus confirming that this parasite caused the outbreak. This role was particularly important because many laboratorians had not had experience identifying Cyclospora.

Another role CDC played was to help State and local health departments conduct the studies that ultimately implicated raspberries as the food item that had made people sick. This aspect of the outbreak investigation focused on the clusters of cases that were associated with specific events. Health departments interviewed the people who had attended the respective events about what they had consumed and compared the responses of the sick and the well people to see how they differed. CDC assisted in various ways for example, by helping to design questionnaires, conduct data analysis, and identify important issues that needed to be addressed in theinvestigations. CDC also assisted some health departments on site with their local investigations.

As more and more clusters of cases were identified, CDC's coordinating role at the national level became increasingly important. CDC sponsored frequent conference calls and a meeting in July 1996 to discuss the findings to date and to help establish priorities for the investigation and future research. Whereas the investigators from individual States and localities focused on their own jurisdictions, staff at CDC repeatedly looked for the patterns that emerged as data from the individual clusters were compiled and analyzed. Fresh raspberries were found to have been served at virtually all the events, and a strong statistical association was found between illness and consumption of raspberries. Although the investigation focused on the clusters of cases, some studies that compared the exposures of sporadic cases and control subjects were also conducted and implicated raspberries.

Another important role played by CDC was that of coordinating public communications as the investigation progressed. CDC helped improve the consistency of the messages that State and local health departments gave to local media. CDC provided a national perspective about the outbreak when interviewed by the national media and published articles in CDC's Morbidity and Mortality Weekly Report to rapidly communicate important findings about the investigation to the public health and medical communities.

Once it was determined that raspberries were the food item responsible for illness, the next step was to determine where they had been grown. This traceback process required close coordination with FDA, State and local agencies, and industry. The first steps of the tracebacks entailed determining where the various events took place and where the raspberries that were served had been bought. The raspberries were then tracked from suppliers and distributors back to importers, exporters, and farms of origin, looking for common themes at each step. The available traceback data implicated Guatemala as the common source for the raspberries. By the time Guatemalan raspberries were implicated, Guatemala's spring export season had essentially ended.

Investigators next tried to determine how the raspberries became contaminated. CDC and FDA sent investigators to Guatemala and to Miami, a major port of entry for imported raspberries, to explore possible modes of contamination. We were able to observe how raspberries were grown, picked, sorted, packed, cooled, transported, and inspected. Because no single packing or storage facility in Guatemala, exporter, type of shipping container, shipment, airline carrier, U.S. port of entry or cargo clearance area, importer, distributor, retailer, or food handler was linked to all events for which we had adequate data about the source of the implicated raspberries, we concluded that some practice or attribute common to multiple farms was the most likely explanation for the outbreak.

Although the mode of contamination was not determined, one hypothesis under consideration is that contaminated water may have been used to mix the insecticides, fungicides, and fertilizers that were sprayed on raspberries. Good laboratory methods for detecting low levels of the Cyclospora parasite on produce such as raspberries or in water and other environmental samplesare not yet available. By the time the clusters of cases were detected, leftover raspberries from the events were not available for testing.

Although the precise mechanism by which raspberries became contaminated was unclear, FDA and CDC provided suggestions to the Guatemalan Berry Commission (GBC) about possible ways to reduce the risk for contamination. The GBC voluntarily implemented various prudent measures to improve water quality and sanitary conditions on farms that were going to export to the United States in subsequent export seasons.

Despite these control measures, another multistate outbreak linked to Guatemalan raspberries occurred in North America in the spring of 1997. CDC learned of this outbreak in early May 1997, when several health departments informed CDC of clusters of cases that were associated with April events. Ultimately, 41 clusters with a total of 762 cases were reported, which were associated with events that occurred April 1 through May 26, 1997, in 13 states, the District of Columbia, and one Canadian province. In addition, 250 sporadic cases were reported for the outbreak period, for an overall total of 1,012 cases in 17 states, the District of Columbia, and two provinces.

Once again, the investigation, which focused on the clusters of cases, implicated fresh raspberries, and Guatemala was found to be the major source of the implicated berries. The outbreak ended shortly after Guatemala voluntarily suspended exportation of fresh raspberries to the United States at the end of May 1997. The fact that another outbreak occurred despite the implementation of various control measures suggests either that the control measures may not have been fully implemented by some farms or that the measures may not have addressed the true source of contamination of the raspberries.

These outbreaks in 1996 and 1997 highlighted challenges related to the investigation of outbreaks of foodborne diseases. Many State and local health departments do not have the necessary infrastructure to conduct outbreak investigations. Also, because Cyclospora is an emerging pathogen, most laboratorians lacked the experience and expertise to identify Cyclospora in stool specimens, particularly during the 1996 investigation. CDC is developing the capacity to use the Internet to assist laboratories in identifying parasites such as Cyclospora in patient specimens. However, many laboratories do not yet have the necessary equipment to take advantage of this technology.

New Challenges New Opportunities

As we draw to the close of the 20th century, we face new paradigms for foodborne disease due to the globalization of the food supply, the large-scale nature of food production and distribution, and the continuing recognition of new foodborne pathogens. CDC addresses these issues by harnessing the technology of electronic telecommunications and computer systems, developing state of the art molecular fingerprinting techniques, integrating its disease prevention and control activities with food safety programs in FDA and USDA, and building active epidemiologic and laboratory-based surveillance programs in collaboration with our State and local partners. However, much work needs to be done to build the necessary architecture for a truly sensitive and responsive early warning network. Building investigative and laboratory capacity in all of our State partners, enhancing our collaborative activities with international partners where, increasingly, some of our food supplies originate, and improving the qualitative and quantitative understanding of critical food safety problems are important components of CDC's response. CDC has been working with the Council of State and Territorial Epidemiologists and the Association of State and Territorial Public Health Laboratory Directors to enhance core surveillance capacity and to assure that the appropriate architecture exists. A 21st century system is needed to confront 21st century challenges.


In conclusion, strong Federal, State, and local public health surveillance networks are the foundation for rapid identification and investigation of infectious disease threats, including those illnesses that are caused by foodborne pathogens. 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.

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