Infectious diseases are the second leading cause of death worldwide, according to current estimates of the World Health Organization (WHO), and are the leading killers of children under five years of age. In spite of tremendous progress made in the United States during the 20th century in reducing infectious disease deaths, when aggregated, such deaths rank third behind cardiovascular disease and cancer in this country.
As Dr. Jeffrey Koplan, director of the Centers for Disease Control and Prevention (CDC), pointed out in a previous column in this series,1 the CDC was established as the Communicable Diseases Center in 1946, succeeding an agency that worked on malaria control during World War II. The agency's mission has broadened dramatically during the last 55 years, but prevention and control of infectious diseases nationally and globally remain an important part of its mission.
The National Center for Infectious Diseases was created at the time of the last major CDC reorganization in 1981. At that time the infectious disease components of the Bureau of Epidemiology, the Bureau of Laboratories, and the Bureau of Tropical Diseases were consolidated to form the new Center. Historically, the CDC had worked with state health departments and international organizations such as WHO as one of the principal partners in infectious disease surveillance and control. In part, the 1981 reorganization of the agency represented an attempt to integrate epidemiology and laboratory science more fully to increase the effectiveness of disease surveillance and prevention programs.
EMERGING INFECTIONS: CONCEPT AND REALITY
In 1992, the Institute of Medicine published a critically important report, Emerging Infections: Microbial Threats to Health in the United States,2 which highlighted the complacency that had developed in the United States regarding infectious diseases, discussed factors that contribute to infectious disease emergence and re-emergence, and drew attention to the inadequacies of public health capacity at the local, state, national, and global levels to recognize and address new and re-emerging diseases. Of importance to the Association of American Medical Colleges (AAMC), the report also drew attention to the barriers of communication and cooperation between medicine and public health, highlighted a number of critical research priorities, and emphasized the importance of training the next generation of clinicians, researchers, and public health personnel as well as the behavioral and social scientists needed to work in partnership to address the complex challenges posed by infectious diseases.
During the six months following the publication of this report, three outbreaks were identified that served to emphasize the validity and importance of its observations and recommendations. These were (1) the multistate outbreak of hemorrhagic colitis and acute renal failure caused by the emerging food-borne pathogen Escherichia coli O157:H7 transmitted by contaminated undercooked hamburgers served by a fast—food restaurant chain, (2) the huge community-wide outbreak of diarrheal illness caused by the emerging waterborne pathogen Cryptosporidium parvum in Milwaukee, and (3) the outbreak of severe acute unexplained respiratory illness initially identified on the Navajo Reservation and shown to be caused by a previously unrecognized hantavirus. These three outbreaks reinforced a number of the observations in the IOM report, emphasized the fact that clinicians play a critical role in the recognition of emerging infectious diseases, and demonstrated that clinicians' linkages with public health officials in their communities and states are critical to ensuring prompt investigation and control of these problems. This lesson has been reinforced repeatedly during the last eight years. In August 1999, an alert infectious disease clinician in Queens, New York, recognized and reported to the New York City Health Department a small cluster of human cases of encephalitis with somewhat atypical clinical features that represented the emergence of West Nile encephalitis in the Western Hemisphere. All of these diseases also raise a range of important research questions, and the steps involved in development and implementation of effective control strategies illustrate the multidisciplinary nature of the partnerships required to respond.
THE CDC'S STRATEGY
Because a number of the recommendations in the IOM report were directed at the CDC, we responded by developing, with input from many partners, an initial CDC strategy to address emerging infectious diseases, which we published in 19943 and updated in 1998.4 The strategy has four goals, which focus on (1) strengthening surveillance and response capacity at the local, state, national, and global levels, (2) addressing important applied research priorities (e.g., identification of risk factors, development of diagnostic tests, identification of virulence factors and genetic determinants of susceptibility, and assessment of effectiveness of rodent and mosquito control strategies), (3) strengthening the public health system, with a particular emphasis on training needs, and (4) implementing effective prevention and control programs. The strategy also includes nine priority areas for special emphasis, including antimicrobial resistance, food-borne and water-borne diseases, vector-borne and zoonotic diseases, and infectious causes of chronic disease. Partnership with the AAMC will be important in addressing each of these priorities.
Two approaches taken in relation to strengthening surveillance and response capacity may be of particular interest to the AAMC. One involves the creation of Emerging Infections Programs (EIPs) in nine states. These are population-based, active research sites that involve partnerships among state and local health departments, academic medical centers, and schools of public health, among others. The EIPs have core projects utilizing common methods focusing on invasive bacterial diseases, including antimicrobial resistance, food-borne disease, and unexplained deaths and severe illnesses of possible infectious etiology. The other approach involves four health care worker—based sentinel surveillance networks involving infectious disease clinicians, emergency departments in academic medical centers, travel medicine clinics, and clinics on both sides of the U.S—Mexico border. Each of these emphasizes strengthening communication and collaboration between clinical medicine and public health.
Since 1999, the CDC has been working to improve public health preparedness to confront the threat posed by bioterrorism. Preparedness requires collaboration and communication between clinical medicine and public health, between human and veterinary medicine and public health, between public health and emergency response communities, and between the infection control and public health communities. Because the diseases that generate the greatest threat (i.e., smallpox, anthrax, plague, tularemia, botulism, and viral hemorrhagic fevers) occur rarely or never in the United States, they are unfamiliar to clinicians, and until recently there had been little ongoing research to provide the tools (e.g., rapid diagnostic tests, effective drugs, new or improved vaccines) to improve preparedness and response capacity.
The events of the nine years since the publication of the IOM report on emerging microbial threats indicate that the microbes will continue to pose difficult challenges. Trends in the factors favoring their emergence and re-emergence (e.g., changes in human demographics and behaviors, poverty and social disruption, changes in land-use patterns, dramatic increases in global travel and international commerce, microbial evolution) generally favor the microbes. In recognition of this reality, the IOM has just embarked on a new study to assess the lessons learned, current preparedness, and future priorities for responding to these challenges.
FUTURE DIRECTIONS AND PARTNERSHIPS
There are currently important opportunities to strengthen local, national, and global preparedness. Microbial threats to health have been identified as a national security issue. The Group of Eight Industrialized Nations (G8) has identified ambitious goals for reducing the global burden of HIV infection, tuberculosis, and malaria by 2010. Private organizations and foundations have made large contributions to global efforts to eradicate and control infectious diseases. A Global Health Fund is being established to support some of these efforts. Pharmaceutical companies are making some important drugs available at no or reduced cost.
Although these steps are cause for some optimism, major challenges remain. There is an urgent need to develop new and strengthen existing critical partnerships. Under the recently developed cooperative agreement between the CDC and the AAMC, there will be opportunities to strengthen the linkages between institutions of medicine and public health, address important research questions through an expanded peer-reviewed extramural research program with an emphasis on prevention, and meet some of the educational and training needs through curriculum modification and use of innovative teaching methods and tools.5 Because of the increasing recognition that we live in a global village and that infectious disease issues, like many others, know no borders, there is increasing appreciation of the need to help address these problems where they occur.6 We should be alert to opportunities to reach out to colleagues and trainees in other countries.
In thinking about what future challenges we may face, antimicrobial resistance and the next influenza pandemic (for which we are overdue) come immediately to mind. In addition, it is likely that we will continue to encounter national and international food-borne disease outbreaks. We will undoubtedly continue to be surprised by the role that microbes play in the etiology of chronic diseases, and will eventually have additional important prevention opportunities as a result. Finally, we should anticipate that we will continue to be challenged by the unexpected, either as a result of naturally occurring disease or an act of bioterrorism.
I would like to encourage persons interested in these issues to subscribe to either the printed or electronic version of the CDC's journal, Emerging Infectious Diseases (www.cdc.gov/ncidod/eid) and to consider participating in the Third International Conference on Emerging Infectious Diseases, to be held in Atlanta March 24–27, 2002 (www.cdc.gov/iceid).