Ann Marie Kimball
Jonathan D. Mayer

The appearance of new infectious diseases and reappearance of old "conquered" ones is alarming to the public and to health experts. Plague in India, Ebola virus in Zaire and Gabon, and leptospirosis in Nicaragua have awakened the public to these health threats. Clusters of these infectious diseases occurred a plane ride away from Seattle. But how does such sensational news affect our own health, and that of our neighbors? How important are emerging infectious diseases (EID) to the Northwest? The answers are complex. This article provides a brief look at some problems the region has already encountered and speculates on the potential for others.

Emerging infections are threatening the welfare of people worldwide. More than 30 new pathogenic microbes have been identified since 1973 and many other diseases have re-emerged (Tables I and 2). The factors contributing to their emergence are population growth, changes in land use, technology and commerce, international travel, changes in organisms, and deterioration of public health protections. These factors are global "megatrends" that simultaneously affect the environment, and also are evident at a regional scale.

The Pacific Northwest is closely connected with East Asia and the Pacific Rim through trade, transport, travel, and immigration. Integration of Pacific Rim economies is increasing as U.S. companies develop new markets in Asia and locate manufacturing facilities abroad, and as Asian companies operate in U.S. markets. Washington generates more revenue from trade with Asia than does any other state, and the ports of Seattle and Tacoma together handle the second largest volume of container shipping in the United States. Also, the region's population has changed in the past two decades. Since the end of the Vietnam conflict we have received tens of thousands of immigrants from Southeast Asia and smaller numbers from elsewhere in Asia, Africa, and Latin America.

Routes of transmission are important in the risk of new infection. Thus, this article addresses the risk of disease emergence through the importation and circulation of new disease carried in by human hosts, inadvertent importation of vectors, and effects of regional economic and social development. First, we review diseases that have already emerged or re-emerged in the Northwest. Then we consider the potential risk from those still far from our borders.

Emerging Infection: A new or newly identified pathogen or syndrome that has been recognized over the last two decades, or that has resulted in new manifestations of infectious disease.

Re-emerging or Resurging Infection: A known or previously identified pathogen or syndrome that is increasing in incidence, expanding into new geographic areas, affecting new population groups, or threatening to increase in the near future.

(Source: Infectious Disease -A Global Health Threat, 1995)

On Our Doorstep

A good example of imported disease is the recent cluster of fluoroquinolone-resistant Neisseria gonorrhoeae in Seattle. This pathogen was first detected in samples from the Philippines that scientists in Hawaii sent to the University of Washington Center for AIDS and STD in 19 9 1. The center participates in a multicenter international surveillance effort for gonorrhea. Cases detected in King County in 1995 were traced to contact with the Philippines. The advance warning that such resistance was occurring in the Pacific enabled local public health officials to limit the spread to just a few persons. Without the early warning, and the resources to react swiftly, disease dissemination could have been much wider.

Tuberculosis (TB) is a resurgent disease that has established a foothold in urban areas with significant concentrations of immigrants and poor or homeless persons. More than 70%, of the TB in King County occurs among the foreign born, and most cases of drug-resistant TB occur in this group. It is not effective or acceptable to close borders to combat disease. Stronger public health surveillance and control practices at home and broad are the answer. The accompanying article on page 8 reviews the quarantine powers of health officers in efforts to control the spread of TB.

Antimicrobial resistance of bacteria is a major problem in the Northwest, particularly for hospitalized patients. The emergence of multiple-antibiotic-resistant enterococci and staphylococci is a trend seen nationwide. Microbes evolve or change to resist antimicrobials when the "pressure" of antibiotic use is high, for example, in hospitals where cost control and quality concerns have narrowed the range of antibiotics used. Cost-saving strategies exacerbate the emergence of resistance in two ways: (1) further limitation of antibiotic choice to save money, and (2) increased presumptive treatment to avoid the costs of culturing patients.

Northwest hospitals also are welcoming patients who come from Asian centers such as Hong Kong and Tokyo for advanced surgical procedures. Even including airfare, it is cheaper for a Hong Kong resident to receive a coronary artery bypass operation in Seattle than at home. To date, these Asian patients have come from countries with high immunization standards, and the hospitals rely on airport health screening to ensure compliance with U.S. regulations. Asian hospitals have the same problems of nosocomial resistance as do Northwest hospitals. However, because resistance patterns differ, "old" microbes in one setting can be "new" in another. Continued emphasis on local nosocomial surveillance systems and communication with colleagues in Asia is an important policy goal to guard against introduction of infections agents.

Microbial contamination of food is another problem, especially because so much of our food supply is imported from outside the region. The well-publicized Escherichia coli 0157:H7 epidemic of 1993 (see Washington Public Health, Fall 1993 and Fall 1995) is a prime example of nonemergent disease with significant public health implications. It reminds us that the mass production of food distributed through national and global networks carries risks as well as benefits. Scientists at the UW School of Public Health led efforts to subtype clinical isolates of E. coli 0 1 57:H7 so as to rapidly identify the source of infection and prevent further epidemics.

The recent New Orleans experience with cholera from uncooked oysters should serve as a sober warning to consumers of seafood. Northwest waters are cholera-free, but cholera will remain endemic in the Americas for the foreseeable future. In 1991 an epidemic occurred in Lima, Peru, via contaminated bilge water from a ship from the Indian sub-continent, plus failure to disinfect the drinking water. This microbial threat remains. The organisms can survive (although not multiply) even in our colder waters. Scrupulous enforcement of responsible bilge handling in our ports is important.

Ships may transport disease vectors in addition to cargo. For example, bilge water may contain pathogenic organisms. Mosquitoes and other insects can survive and breed in containers carrying tire casings. Rats also can stow away, and most ships try to eliminate them through trapping or fumigation so as to receive "derat" decertification.         Port of Seattle

Animal vectors are another channel for the introduction of disease. One of the most recent diseases to appear in the United States, and the Northwest, is hantavirus pulmonary syndrome (HSP) caused by a new strain of hanta virus carried by deer mice. First detected in the Southwest in 1993, 135 cases have now been confirmed in 24 states, including eight cases in Washington (see article on page 9). The lack of effective treatment and the high mortality rate are causes for serious concern.

A Plane Ride Away Diseases endemic to the tropical zones seem an improbable threat to the Northwest, but how safe are we? Could climate changes and other factors increase our vulnerability? Anopheline mosquitoes are the vectors of such infectious diseases as dengue hemorrhagic fever and malaria. According to geographical studies, malaria existed in Oregon's Willamette Valley as recently as the early twentieth century Anopheline mosquitoes, the vectors of malaria, can survive long international flights in the passenger cabins, wheel wells, or cargo compartments of airplanes. If they arrive at a temperate destination during the summer, they can survive and reproduce. Clusters of cases of "airport malaria" have occurred near international airports in the New York City area, Brussels, Belgium, and Geneva, Switzerland. However, the Northwest's present climate is too cold for anopheline mosquitoes, so malaria, if introduced, would remain within a few kilometers of the Seattle, Portland, or Vancouver, B.C., airports and affect only a few travelers or local residents, and then only during the height of summer. The situation with dengue fever is not as reassuring. Its vectors, Aedes aegypti and Ae, albopictus, can be transported inadvertently on aircraft and in barges or containers carrying tire casings. Aedes is hardier than Anopheles, and dengue is spreading northward. This movement of the Aedes spp. into the United States from Latin America is major concern. Indigenous acquired cases have been reported in southern Texas. Entomologists believe that the Northwest summer climate (20'C isotherm) can support Aedes and the transmission of dengue. A worldwide concern is the potential for global warming due to the depletion of the ozone layer and the "greenhouse" effect of increasing carbon dioxide in the atmosphere. Some scientists believe our planets mean annual temperature will warm by 2-3'C over the next 50 to 100 years. Were this to occur, the environment would be more hospitable to many vectors and our susceptibility to vector-borne disease would increase, even in the Northwest.

How Do We Protect Ourselves?

According to the International Disease Regulations, only plague, yellow fever, and cholera are quarantinable" diseases. However, the meaning and effectiveness of quarantine has changed in the era of modern travel. Airport screening protocols (see article on page 6) offer some measure of protection against disease introduction by immigrants and refugees, who are required to present health certificates to customs officers. Certificates are not required for tourists and business travelers, it is clear from the procedures for airport screening for plague and Ebola virus, and for the plague screening during the Indian epidemic of 1994, that we lack the means to effectively deal with disease introduction through travel.

Again, more stringent exclusion or quarantine is not practical or desirable. How then can we be sure that we are safe from imported diseases? Disease introduction is a threat primarily in the absence of basic public health measures in the newly exposed population. High immunization levels in our population decrease the likelihood of disease propagation from vaccine-preventable disease such as measles, polio, and diphtheria that may arrive in travelers. Similarly, were a traveler to bring plague to Seattle, our best defense would be early detection and reporting of the case contacts to the local health department, facilitated through communication among public health agencies in other communities closely connected to ours by travel and trade. Just as for the environment, the slogan for such public health vigilance should be "think globally, act locally."

New Local Initiatives

At the University of Washington we have established an Emerging Infectious Diseases Working Group, one of the first in the nation, to address threats posed by EID and diseases that are becoming resistant to antibiotics. The group has about 150 members and includes faculty in medicine, public health, molecular biology, anthropology, zoology, and geography, and colleagues from local and state health departments. The interdisciplinary nature of the group stems from experience with the AIDS pandemic and the awareness that a broad response is needed to address a global pandemic of new infectious diseases. The Working Group is sponsoring speakers and panels on EID topics and is organizing work groups for grant applications and disease surveillance. Enhancing interdisciplinary research at the community and international level is a central objective.

In summary, the global phenomenon of newly emerging infections is highly relevant to residents of the Northwest. We are an airplane flight away from exotic diseases, our medical practices continue to put selective pressure on bacteria to become resistant to antimicrobials, and our own continued development as a region could increase our potential susceptibility to infectious diseases. The key defense in this scenario must be a strong and vigorous local public health response. Increasing our public health links with our neighbors and trading partners around the Pacific will be an important element.

Recommended Reading

Centers for Disease Control and Prevention: Exposure of passengers and flight crew to Mycobacterium tuberculosis on commercial aircraft 1992-19 5. MMWR 1995;44 137-140.

Brandling-Bennett AD, Pinheiro F: Infectious diseases in Latin America and the Caribbean: Are they really emerging and increasing? Emerging Infectious Diseases 1996;2:59-(51.

Cliff A. Haggett P: Disease implications of Global Change. Ann NY Acad Sci 1994, 740:206-223.

Garrett L: The return of infectious disease: Foreign Affairs 1996;75: 6-79.

Infectious Disease -A Global Health Ticket. Report of the National Science and Technology Council Committee on International Science, Engineering, and Technology Working Group on Emerging and Reemerging Infectious Diseases, September 1995. For further information contact: Centers for Disease Control and Prevention, National Center for Infectious Diseases, (404) 639-2603.

Institute of Medicine: Emerging Infections: Microbial Threats to Health in the United States. J Lederberg, RE Shope, SC Oaks, Jr (Eds). Washington, DC: National Academy Press, 1992.

McNeill WH: Plagues and Peoples. New York: Anchor Press, 1976.

Patz JA, Epstein PR, Burke TA, Balbus JM: Global climate change and emerging infectious diseases. JAMA 1996;275:217-223.

Pinner RW, Teutsch SM, Simonsen L, et al: Trends in infectious diseases mortality in the United States. JAMA 1996;275:189 193.

Roizman B (Ed): Infectious Diseases in an Age of Change: The Impact of Human Ecology and Behavior on Disease Transmission. Washington, DC: National Academy Press, 1995.

Zucker JR: Changing patterns of autochthonous malaria transmission in the United States: A review of recent outbreaks. Emerging Infectious Diseases 1996;2:37-43.

Authors

Ann Marie Kimball, M.D., M.P H., is an associate professor of health services at the UW School of Public Health and Community Medicine.

Jonathan D. Mayer, Ph.D., is a professor of geography and adjunct professor of medicine (infectious diseases), family medicine, and health services at the University of Washington.

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