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Institute of Medicine (US) Forum on Emerging Infections; Davis JR, Lederberg J, editors. Public Health Systems and Emerging Infections: Assessing the Capabilities of the Public and Private Sectors: Workshop Summary. Washington (DC): National Academies Press (US); 2000.

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Public Health Systems and Emerging Infections: Assessing the Capabilities of the Public and Private Sectors: Workshop Summary.

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2Epidemiological Investigation


Emerging infections continue to disrupt the health care system and are becoming increasingly complicated to detect and treat successfully. In addition, the public health system is continually reminded of the challenges posed by the unexpected, whether it is the next influenza pandemic or a bioterrorist act. In 1988 the Institute of Medicine (IOM) recommended that “every public health agency regularly and systematically collect, assemble, analyze, and make available information on the health of the community, including statistics on health status, community health needs, and epidemiologic and other studies of health problems” (IOM, 1988, p. 141). Thus, one of the essential public health services is the diagnosis and investigation of health hazards in the community. Health departments at the federal, state, and local levels, often with the aid of the academic community, can perform these functions if they have the appropriate level of resources, adequately trained personnel, and established systems of reporting and communication.

Each sector offers unique capabilities, and each sector faces some common and uncommon challenges, but most infectious disease outbreak investigations follow the same general approach: (1) identification of the circumstances that indicate the need for an investigation (e.g., more than the expected number of cases of a particular disease); (2) investigation; (3) determination of the cause of the circumstances (i.e., the reason that the excess cases of disease occurred); and (4) response, which usually includes the control of the outbreak, and recommendations and coordination of response—both public and private—for the prevention of further disease. Within each investigation are several components which may include, but are not limited to epidemiological, laboratory, and environmental assessments. Each component may also require coordination at several levels, from the local to the state, private, and federal. In general, federal resources, through the Centers for Disease Control and Prevention (CDC) and the U.S. Food and Drug Administration (FDA), are available to assist in investigations, but they only do so if state and local public health agencies have in place the infrastructure to detect and report unusual disease occurrences. Concise and timely communication between each component is critical to a good investigation.


, M.D.

Associate Director for Epidemiologic Science, National Center for Infectious Diseases, Centers for Disease Control and Prevention

Although the crises attendant with periodic infectious disease outbreaks serve as a reminder of the importance of public health, media attention on the successful investigation and control of outbreaks also contributes to the common misconception that the infrastructure available to meet public health needs is sufficient. However, although media attention has been instrumental in keeping many infectious diseases in the forefront of public consciousness, such misconceptions about the sufficiency of the infrastructure contribute to greater expectations on the part of the public and those who control resources.

Investigations are more complex in nature because of a variety of new pathogens and risk factors (e.g., travel, food imports, technological innovation) increased public and media attention, their significant economic and political consequences, and because they are more likely to cross state and international jurisdictional boundaries. The ability to quickly recognize and respond to widely dispersed disease outbreaks is a particular public health management challenge.

The tools available to recognize and respond to disease outbreaks have improved in recent years. There are now computerized databases which allow outbreaks to be more rapidly recognized, and electronic mail and the Internet allow information to be more rapidly shared. As one example, CDC now develops and shares with public health officials a weekly line listing of Escherichia coli O157:H7 outbreaks that have been recognized. This allows seemingly disparate outbreaks to be potentially linked. The development and dissemination of molecular fingerprinting has virtually revolutionized our understanding of the epidemiology of infectious diseases, and has been especially useful in outbreak recognition and investigation. This technology allows laboratories to subtype pathogens, and for foodborne pathogens, to electronically submit pattern analysis to a centralized database maintained by CDC. Real-time analysis of submitted data allows recognition of outbreaks when they are still small, and has allowed us to recognize outbreaks which previously were unlikely to have been identified. Early recognition and prompt investigation has likely led to prevention of large numbers of illnesses, especially those related to foodborne disease. However, identification of outbreaks when they are small can prove a challenge for investigators to identify the source and risk factors.

In the United States, outbreak investigation and control is the responsibility of state and local health departments. When outbreaks are small and focal in nature, as they usually were in the past, this arrangement is adequate. However, it produces challenges in an era of a globalized food supply and international travel when outbreaks cross jurisdictions. CDC’s federal role is to support the investigations conducted by the states and localities through the provision of technical assistance and resources. The most intensive CDC support is through the epidemic assistance (Epi-aid) mechanism where a team (including an Epidemic Intelligence Service epidemiological trainee) goes into the field to assist the state; there are also international Epi-aids.

However, CDC provides lesser degrees of assistance to state and local jurisdictions in hundreds to thousands of other outbreak investigations annually. This assistance can take a number of forms. One is provision of advice from technical and disease experts, who may go into the field to provide assistance. Another is through specialized diagnostic and laboratory investigations to determine the cause of illness or to subtype or sequence pathogens. CDC can also provide assistance in study and questionnaire design, and set up computer programs to enter data. CDC, in collaboration with the World Health Organization has developed an integrated DOS-based (but Windows™-compatible) free software package, Epi-Info, to assist in outbreak-related activities. The package allows the user to design questionnaires, and receive assistance in epidemiological study design, data analysis, and report writing. This software is used extensively both in the United States and abroad.

Finally, CDC can also provide assistance in implementation of control measures, including direct provision of materials such as vaccines or biologics. For example, if there is an outbreak of hepatitis A or B and the local jurisdiction has difficulty finding adequate supplies of immunoglobulins, CDC can help locate supplies in other parts of the country.

An increasingly important role at the federal level is outbreak coordination and notification of other jurisdictions about an outbreak. It is no longer uncommon for domestic outbreaks to involve 20 or more states, any one of which may have too few cases of illness to conduct meaningful independent investigations. Recent examples of such outbreaks include cyclosporiasis associated with imported fresh raspberries, salmonellosis associated with contaminated cereal, and listeriosis due to contaminated hot dogs. In such instances, consistent case definitions for illness must be applied, standard questionnaires must be employed, selection of controls for case-control studies must be similar, specimen collection and disposition must be consistent, and data must be shared and pooled.

Sister federal agencies also play a vital role in outbreak investigations, particularly the Department of Agriculture’s public health agency, the Food Safety and Inspection Service (FSIS) and the Department of Health and Human Service’s Food and Drug Administration (FDA). Both FSIS and FDA play a role in foodborne outbreaks because of their regulatory oversight of all food products, the former agency responsible for meat, poultry and egg products, and the latter responsible for all other food products. In 1997, FSIS’s Office of Public Health and Science created the Epidemiology and Risk Assessment Division which includes eight field epidemiologists who assist states, local jurisdictions, and CDC with trace-back efforts during outbreaks where FSIS-regulated products have been implicated. In recent years, FDA has tried to improve the coordination of its response to multi-state outbreaks with CDC and other federal agencies. Because food-borne outbreaks frequently involve low-level sporadic contamination of widely distributed foodstuffs, often in food from other countries, FDA must deal with multiple federal agencies and jurisdictions. The FDA Division of Federal-State Relations aims to conduct outreach and coordinate such efforts.

CDC has attempted to enhance the capacity of state and local partners to conduct surveillance for disease outbreaks in a number of ways using resources allocated for emerging infectious diseases. One is through improved in-house laboratory and epidemiological expertise. The second is through provision of resources to state health departments. One category of support is known as Epidemiology and Laboratory Capacity (ELC) cooperative agreements, which states have used to build epidemiological capacity, improve laboratory infrastructure, and electronically link local health departments. The second category is the Emerging Infections Program (EIP) sites, which conduct more active disease surveillance and epidemiological studies, including the FoodNet system to monitor the incidence of foodborne diseases. The third category is the development of the PulseNet system for molecular fingerprinting of enteric pathogens.

Working with the Council of State and Territorial Epidemiologists (CSTE), CDC has developed a number of strategies aimed at accomplishing multijurisdictional investigations while respecting state autonomy. These include development of a coordination checklist, which allows state and local agencies to determine when to inform others of an outbreak and when the outbreak may have more widespread implications. CDC has also established a partnership with state epidemiologists to review available data during an outbreak and make determinations about the required public health response, as well as serve a quality control function by reviewing the investigation once it is concluded. These deliberative groups, which are ad hoc, serve the important purpose of aiming to balance local needs with national public health obligations. To allow better notification of potentially involved jurisdictions, CDC is developing a computer program known as Epi-X, which will allow users to input data on outbreaks in their jurisdiction into a centralized database, simultaneously informing other public health officials of the occurrence. This should enhance information sharing and notification, and allow the development of a database on disease outbreaks, their risk factors, and control measures.

While these efforts have significantly improved the United States, ability to recognize and respond to disease outbreaks, there is still substantial room for improvement. Not all states currently participate in the ELC or PulseNet system, and their capacity to conduct investigations is limited. The international capacity for outbreak recognition and response is also spotty, although WHO is working toward improvements in this area. In the outbreak setting, successful investigations require a coordinated, rapid response. To the degree that one of the involved jurisdictions cannot meaningfully play their role, this goal cannot be completely achieved.


, M.D.

Iowa Department of Health, and President, Council of State and Territorial Epidemiologists

One of the essential public health services at the state level has been identified as the ability to diagnose and investigate health problems and health hazards in the community. State health departments are often on the front line of outbreak investigations, and the information concerning potential outbreaks can come from many sources, such as the medical care system, public agencies, or other public health entities. At times, the recognition of potential outbreaks can be coincidental and informal such as two physicians realizing that they had seen patients with similar but unusual syndromes, as occurred with eosinophilia myalgia syndrome. At other times, the identification of an outbreak occurs via established public health surveillance systems. After the identification of a potential outbreak, the investigation starts to reveal the cause or causes of the outbreak, and in the end, recommendations are made to stop the outbreak and to prevent future illness.

Disease surveillance systems are usually population-based and can be either active (e.g., calling hospitals to find cases of eosinophilia myalgia syndrome) or passive (laboratories mailing reports of infectious diseases to the health department). Although, active surveillance is expensive, it usually results in more accurate data, but passive surveillance, even when only as few as 10 percent of cases are reported, can be adequate for tracking disease trends. Sentinel surveillance systems rely on reports of a few cases of disease whose occurrence suggests that preventive or therapeutic care efforts need to be adjusted. For diseases like influenza, sentinel surveillance can be relatively inexpensive and yet have the ability to obtain timely and valuable information.

A variety of diseases are made legally “reportable” to state health departments, a requirement that contributes greatly to the ability to track the health of the population under surveillance. These reportable diseases include infectious, occupational, chronic, and environmental diseases, as well as conditions such as injuries, birth defects, and cancers. Most state public health systems also require the reporting of outbreaks, unusual syndromes, and uncommon diseases, and include a provision that allows “emergency” or research-related reporting in special circumstances (e.g., to investigate the possible association between Guillain-Barré syndrome and influenza vaccination in the early 1990s).

Although each investigation is unique, most state-level investigations require basic components to ensure a timely and appropriate conclusion:

  1. Epidemiological component. The determination of a cause of an outbreak usually requires the use of accurate epidemiological methods to ensure the collection of unbiased data, the use of appropriate statistical methods in the analysis of the data (often with the use of computer software such as Epi-Info [computer software developed by CDC]), and the correct interpretation of the analysis results.
  2. Laboratory component. The ability to collect specimens, whether clinical specimens from patients, environmental specimens from food or water, or targeted specimens (such as the filter of a whirlpool associated with cases of Legionnaires’ Disease), is a critical component of the investigation. The ability to have these specimens appropriately analyzed is often critical, particularly if regulatory authority needs to be invoked, for example, to recall food products on the market.
  3. Environmental component. The information provided by the environmental health engineer’s investigation is instrumental for determining what environmental risks were present. For example, the engineer’s information can determine if the chlorination unit at the municipal water supply was working correctly or if the oven used to bake the casserole at a local restaurant was hot enough to kill all pathogenic bacteria.
  4. Effective communication. The final and often most critical component is effective communication. The results of the investigation must be communicated and the appropriate individuals must be educated about the actions needed to reduce the risk of further illnesses.

Frequently, an incident that begins at the state or local level requires national response as it becomes evident that the outbreak has crossed state borders. An example of this occurred in the summer of 1996 when members of the National Guard from Iowa became ill after returning from 2 weeks of training at Camp Chaffee, Arkansas. When medical officials at the National Guard became aware of the situation, they contacted the Iowa Department of Public Health to report a possible outbreak, to solicit help in appropriate laboratory testing of blood specimens, and to seek epidemiological advice. The symptoms reported by the members of the Guard were consistent with those of tick-borne illnesses, such as ehrlichiosis or Rocky Mountain spotted fever, both of which are known to occur in Arkansas but which occur only rarely in Iowa. The situation was complicated by the fact that many members of the Guard had donated blood after being exposed to the ticks, but before becoming ill, thus potentially spreading the disease to the blood recipients.

After the Iowa Department of Public Health confirmed that the illness was a tick-borne disease, CDC was contacted for assistance, since it became apparent that the Guard members from other states were also attending training sessions and the blood recipients, who resided in many states, were at risk of developing disease. CDC played an essential role by coordinating and assisting the investigations in several states and took primary responsibility for recalling and determining the safety of the donated blood. This investigation involved several states and CDC as well as other national entities such as the National Guard, the Red Cross, and other organizations concerned with the safety of the blood supply. The epidemiological investigation included interviewing ill and well members of the guard, obtaining blood specimens, and tracing donated blood units. The environmental investigation involved inspection of the Fort Chaffee site for the presence of ticks and other risk factors and the retrieval of ticks for identification and testing. The laboratory component involved testing of blood specimens from members of the guard, blood recipients, and ticks.

The results of the combined investigations were recommendations to the National Guard and Fort Chaffee on methods for reducing the risk of transmission of tick-borne diseases and obtaining a better understanding of the risks of transmission of tick-borne diseases via blood transfusion. This one investigation, however, tapped all available epidemiological resources in Iowa for its duration. It illustrates how outbreaks within an individual state can quickly become a challenge at the national level as well.

To ensure that state-level responses to outbreaks of illness are adequate, appropriate, timely, and efficient, surveillance systems for diseases of public health importance must be in place. There need to be adequate resources at the local, state, national, and, occasionally, international levels to respond to and investigate these outbreaks. The needed resources include both adequately trained personnel and resources such as computers, laboratory testing reagents, and environmental monitors. When all of these components come together, the state can be assured that it has the best ability to identify, investigate, and address problems affecting the public’s health.


, M.D., M.P.H.

Director, Infectious Disease Epidemiology Program, West Virginia Bureau for Public Health

The local public health department’s role in an outbreak investigation is vital. It is most often the agency charged with maintaining surveillance systems that detects outbreaks and that receives the first call for a response when an outbreak occurs. In most outbreaks, the best opportunity for collection of epidemiological data and laboratory specimens as well as for applicable environmental investigations is in the first few hours to days of the outbreak. These become critical roles of the local health department, for on-site state and federal involvement is often, at a minimum, 1 to 2 days away.

Nevertheless, many barriers to the appropriate accomplishment of this essential public health service exist. Detection and reporting systems remain inadequate in many locales. Many local public health agencies cover small jurisdictions (often jurisdictions with populations under 15,000 to 20,000) and are staffed by a nurse, a sanitarian, a clerk, and a part-time health officer. Thus, a limited number of staff members are available for outbreak investigations because they meanwhile are needed to maintain other critical functions. In addition, it is difficult to develop and maintain the skills required to conduct an investigation given the infrequency of outbreaks’ occurrence. Finally, a low administrative priority is often given to outbreak investigations since little funding or planning is dedicated to what is often a rare and intermittent event.

As a bare minimum, local health officials need basic investigational skills in questionnaire design, interviewing techniques, and collection of environmental and clinical specimens. They need computer, media, communications, and coordination skills. Importantly, they need to extend these skills beyond classic food-borne outbreak investigations, because they are increasingly being called to investigate respiratory illnesses in school systems, occupational exposures, nosocomial infections, day care center outbreaks, and so on. Electronic communications systems need to be strengthened so that information about outbreaks can be shared and resources for use during the outbreak can be obtained. Finally, many core-capacity documents, grants, and so on, explicitly define system expectations to the state level only (or combine the expectations for the state and local levels). There is a need to better define expectations about local health department capacities in outbreak investigations.

In sum, local health departments, which are often the first to be called when an outbreak occurs, are often the least equipped to respond. Current inadequacies can be overcome with the assistance and guidance of state and federal agencies and with enhanced collaborations with local agencies. General principles that should be kept in mind when developing solutions to these issues include the following: (1) Local health departments want to and must remain involved with outbreaks in their jurisdictions. In most, the legal authority for outbreak investigations rests at the local level. (2) Training must be designed to maintain as well as develop these skills, and training must be long-distance accessible. (3) Most local health departments already have working relationships with states (although they may be administratively autonomous). (4) Local health department staff members are open to guidance, direction, and development of new skills but want clear expectations and adequate resources to accomplish them. (5) Building and maintaining the local capacity to detect and respond to an outbreak can dramatically strengthen the public health system’s ability to respond to larger epidemics (e.g., a flu pandemic or a bioterrorist attack).


, M.D.

Epidemiologist, Portland Veterans Affairs Medical Center

Historically, clinicians have played a central role in outbreak investigations and surveillance. Long before the causative agents for infectious disease were known, the observations of medical practitioners served to alert the community to unusual occurrences. Even after the etiologies of infectious diseases have been unraveled and laboratory tests made available, clinicians still play an essential role in providing cases for study and assisting in some epidemiological investigations. Often, however, physicians are not sure when and where to report suspicious cases of disease, are unaware of the need to collect and forward specimens for laboratory analysis, and may not be educated regarding the criteria used to launch a public health investigation. Often, there is lack a of communication among public health agencies and community physicians.

To bring these two sectors together, a number of obstacles need to be overcome, including addressing the historical biases that each group holds about the other, improving communications channels, providing public health offices with the financial resources they need to establish and maintain professional working relationships with the physician community, and educating physicians about the need to interact with public health agencies.

In 1995 CDC announced the Cooperative Agreement Program for Provider-Based Emerging Infections Sentinel Networks in support of an approach that aims to overcome some of the obstacles that impede practitioner involvement in the epidemiological investigation process. The program had its origin in a CDC plan that addressed emerging infectious disease threats; listed under a disease surveillance goal was the aim of establishing two physician-based sentinel surveillance networks to detect and monitor emerging infectious diseases. In 1995 CDC made awards to (1) the Infectious Diseases Society of America (IDSA), which has 4,700 active members, half of whom are clinical consultants in infectious diseases; (2) EMERGEncy ID NET, a group of academic emergency department physicians; and (3) GeoSentinel (funded in 1996), a group of travel medicine physicians, including some outside the United States, who joined together to report on phenomena related to emerging infectious diseases.

In 1996, the IDSA created the Emerging Infections Network (EIN), which now has more than 700 active members. The strength of EIN lies in its members, who have trained in internal medicine or pediatrics, have completed 2 or more years of subspecialty training in infectious diseases, and serve a varied patient population. EIN members are geographically dispersed and communicate regularly with clinical microbiologists and pharmacists, who help them determine which antibiotics are being used in health care facilities and why (see Figure 2-1).

FIGURE 2-1. Geographical distribution of Emerging Infections Network members.


Geographical distribution of Emerging Infections Network members. Source: Infectious Diseases Society of America, 1998. SOURCE: IDSA Emerging Infections Network, unpublished data.

EIN aims to (1) detect unusual clinical events (2) assist in the identification of possible cases and outbreaks being investigated by CDC and other public health authorities, (3) acquire knowledge about the use of diagnostic tests for specific syndromes in different parts of the country and provide preliminary estimates about morbidity and mortality, (4) collaborate in research with CDC and other public health agencies, and (5) educate and communicate with health care professionals through periodic and ongoing requests for information on a specific topic. Sometimes EIN makes urgent queries and requests assistance with outbreak investigations, for example, by requesting a 24-hour response on experiences with febrile reactions after once-a-day gentamicin use related to possible endotoxin contamination. When appropriate, EIN sends its initial observations to CDC and to state health departments. It also sends preliminary reports back to its members within a month of issuing the query. Results of queries are published on the World Wide Web (


, M.D., M.P.H.

Dean, School of Public Health, University of North Carolina at Chapel Hill

Academic public health institutions are a vital component of the global response to emerging infections. The roles that these institutions play flow directly from their core missions of education, research, and public health practice.

Academic public health institutions maintain primary responsibility for producing a public health workforce that is skilled in responding to emerging infections. This requires (1) fostering an awareness of emerging infections and their public health importance among students in schools of public health, (2) training students in the most advanced concepts and methods for disease surveillance and epidemiological investigation, and (3) ensuring student exposure to and understanding of real-world issues in the prevention, detection, treatment, and control of emerging infections through targeted field experiences and collaboration with public health organizations.

Academic institutions must also assume a primary role in keeping practicing health professionals informed of new knowledge, practices, and technologies that can be used to respond to emerging infections. Schools must capitalize on new technologies in continuing education, distance learning, and executive training that make use of the Internet, wide-area computer networks, and satellite communications. To be effective, these activities must be carried out in close partnership with national, state, and local public health organizations.

Academic public health institutions play central roles in strengthening and expanding the scientific base to identify and respond to emerging infections. This is done through laboratory research, in partnership with researchers in the basic medical sciences, especially microbiology, to develop an understanding of the basic biology of emerging pathogens. Epidemiological research identifies emerging infections in populations to discover the mechanisms of transmission, with the eventual goal being to develop interventions for the prevention, detection, treatment, and control of the infections. This area of research includes the development of new surveillance methods and the use of biostatistical models in predicting disease progression and transmission.

Clinical research further elucidates the clinical practices and technologies that are most effective in preventing, diagnosing, and treating emerging infections. Primarily academic medical schools lead these efforts, often with close collaboration from epidemiologists and biostatisticians in schools of public health.

Behavioral research interprets the roles of human decision making and interactions in the prevention, treatment, and control of emerging infections. Academic public health institutions can bring together the concepts and methods from a variety of behavioral science disciplines—including psychology, sociology, economics, demography, and geography—and apply them to the study of emerging infections.

Health services research, operations research, and program evaluations identify the most effective ways of communicating information, exchanging data, and coordinating efforts in disease prevention, treatment, and control across organizations. This research is critically important as the health system grows more complex, with public- and private-sector organizations sharing responsibilities in disease control and prevention.

Public health policy research informs the policy decisions faced by national, state, and local public health officials in addressing emerging infections. This research can help to answer questions about the public benefits and risks of policies, such as those affecting the privatization of laboratory services, the reporting requirements for public- and private-sector health care providers, and the privacy and confidentiality concerns of patient health and health care information.

It is imperative that academic public health institutions carry out all these research activities in close collaboration with academic medical institutions and that both entities share the knowledge and expertise in emerging infections that each brings to bear. For example, epidemiologists in schools of public health must work closely with colleagues in medical school divisions of infectious disease to elucidate biological pathways and transmission mechanisms.

Academic public health institutions also have important roles to play in providing technical assistance, advice, and consultation to the organizations involved in responding to emerging infections. These activities ensure that findings from scientific research are disseminated, adopted, and implemented within these organizations. Key activities include the following:

  • assisting in the design and operation of governmental surveillance and early-warning systems,
  • coordinating surveillance and reporting systems across governmental boundaries,
  • supporting the adoption and use of new surveillance techniques,
  • assessing the preparedness of health care providers to identify and report on emerging infections at the local level, and
  • advising organizations on how best to respond to changes in the organization and to changes in the financing of health services and the effects of these changes on disease surveillance capacities.

Traditionally, schools of public health have worked most extensively with state and local health departments, and the entities are natural partners in public health education, research, and practice. A much broader array of organizations is now involved in the practice of public health generally and in the response to emerging infections more specifically. Academic institutions must find ways in which they can work more effectively with this broader array of organizations, including commercial laboratories, managed care plans, hospitals, and private physicians.



Delivered in absentia.

Copyright © 2000, National Academy of Sciences.
Bookshelf ID: NBK100248


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