Book Review

Emerging Infections: Microbial Threats to Health in the United States

N Engl J Med 1993; 329:1432-1433November 4, 1993

Article

Emerging Infections: Microbial Threats to Health in the United States
Edited by Joshua Lederberg, Robert E. Shope, and Stanley C. Oaks, Jr. 294 pp. Washington, D.C., National Academy Press, 1992. $34.95. ISBN: 0-309-04741-2

Three decades ago this book would have been marketed as science fiction. Smallpox was on the verge of extinction, and health officials targeted measles, malaria, and other diseases for eradication. Powerful vaccines and drugs were poised to defeat microbial foes, one after another., and then the world seemed to change. Infectious diseases appeared and recrudesced in seemingly unpredictable, capricious ways.

In early 1991 the Institute of Medicine convened a distinguished committee to study emerging microbial threats, with a focus on threats to public health in the United States. The main premise of the study was that “anticipation and prevention of infectious diseases are possible, necessary, and ultimately cost-effective.” The resulting report, published here in book form, focuses on diseases that have emerged within the past two decades and defines emerging infectious diseases as clinically distinct conditions that are increasing in incidence; reemerging diseases are those that have reappeared after a decline in incidence. Emergence can be a consequence of the appearance of a new microbe, the recognition of a previously undetected disease, or changes in the environment that permit microbes to enter a human population.

The book is rich with familiar stories from remote and recent events. With examples ranging from plague to tuberculosis, the first chapter provides convincing evidence of the past importance and current threat of infectious diseases. The committee identified six major factors that lead to the emergence of infections: human demographics and behavior, technological advances, economic development and land use, international travel and commerce, microbial adaptation, and breakdown of public health measures. A detailed discussion containing numerous examples underscores the complexity of the emergence of diseases.

A large section of the report is devoted to “addressing the threats.” The approach is two-pronged: recognition of the threats through expanded surveillance activities and the use of interventions, which include research and training, vector control, vaccine and drug development, and public education. The committee lays out 14 specific recommendations to improve the U.S. capacity to respond to emerging infections. Many involve expanding or building on existing systems. The main message comes through repeatedly: existing institutions and resources fall far short of what is needed to deal with current threats, and anticipating and preventing epidemics is far less costly than curbing epidemics. Although public health advances in the United States have been achieved as a result of health crises (often epidemics or fear of them), better surveillance and planning should lead to scientific advancement without the crises.

At the outset the committee decided to focus on problems that threaten the United States. But in the late 20th century, few infectious diseases remain restricted to one geographic area. Through the movement of persons, animals, and materials, most infectious diseases can appear almost anywhere, regardless of their point of origin. In recognition of the global reach of many of the emerging infections, numerous examples are drawn from diseases that exist on other continents. There appears to be some idiosyncrasy in the choice of diseases that make up the list of threats. The principle that guided inclusion or exclusion is not always explained clearly.

The report rightly stresses surveillance as a critical part of the recognition of emerging diseases. The discussion of other approaches could be strengthened. I would favor more emphasis on basic research to identify reasons for emergence in order to allow predictions about the types of pathogens and geographic areas most likely to contribute to emerging diseases. Studying the emergence of diseases requires a broad understanding of ecology, including the social, political, and climatic context as well as interactions between diseases. Mention of these aspects is limited. The report would also have benefited from more discussion of animals as a source of human microbes and a call for more basic research on what allows a microbe to cross from one species to another.

Principles of the emergence and eradication of diseases go hand in hand. A section laying out the prerequisites for the establishment of a disease in an area (e.g., malaria) and the characteristics of a pathogen that make eradication feasible (e.g., smallpox) would help pull together general principles suggested by the examples. The eradication of smallpox, mentioned in several sections, remains an extraordinary feat. A description of the biologic, clinical, and epidemiologic characteristics of the virus that made this feasible (and that make the eradication of many viruses unlikely or impossible) would promote a clearer understanding of the basic principles that underlie the achievement.

The reasons for the emergence of each disease are listed. Some are overly simplistic or limited and may mislead the reader who skips some of the text. For tuberculosis, for example, immunosuppression is the only factor listed for emergence in the table and in the catalogue in the appendix, though other factors are discussed in the text. Increased use of broad-spectrum antimicrobial agents should be included among the reasons for the emergence of Clostridium difficile.

It is sobering to note that a single pathogen -- the human immunodeficiency virus (HIV) -- alone or in part accounts for the emergence (or reemergence) of Pneumocystis carinii pneumonia, toxoplasmosis, cryptosporidiosis, and microsporidia and is a major contributor to the reemergence of tuberculosis. In the list of emerging pathogens I would have included Mycobacterium avium complex, histoplasmosis, coccidioidomycosis, and leishmaniasis, all of which also have important interactions with HIV.

Humans occupy a fragile position in this biosphere. That diseases emerge or reemerge should come as no surprise. The response should be concern and scientific inquiry, not bewilderment and complacency. Given technological advances, ease of travel, and the myriad changes in the environment, we can anticipate that diseases will continue to emerge and that the rate at which they emerge may accelerate. Human activities propel changes that lead to the emergence of diseases. This book makes clear the multiplicity of origins of emergence and the complexity of finding workable interventions. This report is intended as a wake-up call and a blueprint for action. Those who miss this ring of the alarm have only to read the morning paper or turn on the radio to be reminded that the list of emerging diseases is growing faster than the list of those being eradicated. This is an important and compelling report that deserves to reach a large audience.

Mary E. Wilson, M.D.
Mount Auburn Hospital, Cambridge, MA 02138