Emerging Infectious Diseases: Public Health Issues for the 21st
Sue Binder, 1* Alexandra M. Levitt, 2
Jeffrey J. Sacks, 3 James M. Hughes 4
Infectious diseases are the third leading
cause of death in the United States and the leading cause worldwide. As the new millennium
approaches, the public health community must replenish capacity depleted during
years of inadequate funding while simultaneously incorporating new technologies
and planning for the longer term. Among the challenges facing the public health
community is the need for coordinated, global, multisectoral approaches to
preventing and controlling complex infectious disease problems.
1 Division of Parasitic Diseases,
National Center for Infectious Diseases
(NCID), Centers for Disease Control and Prevention (CDC), F-22, 4770 Buford Highway,
NE, Atlanta, GA 30341, USA.
2 Office of the Director, NCID, CDC, 404 Sixth Avenue, Third Floor,
Brooklyn, NY 11215, USA.
3 National Center for Injury Prevention and Control, CDC, K-63,
4770 Buford Highway, NE, Atlanta, GA 30341, USA.
4 NCID, CDC, C-12, 1600 Clifton Road, NE, Atlanta, GA 30333, USA.
* To whom correspondence should be addressed.
After World War II, there was widespread optimism in the United States that good
sanitation, vaccines, and antimicrobial agents would conquer infectious diseases. However, public health successes of
the 1960s and 1970s were followed in the 1980s and early 1990s by ominous
developments, such as the recognition of the extent of the HIV/AIDS epidemic
and the resurgence of diseases such as tuberculosis.
Part of this backslide occurred because of decreased funding for and subsequent erosion
of the public health infrastructure (1, 2).
Starting in 1992, a series of reports called for prompt U.S. government
action against emerging infectious diseases (EIDs) (3-5). As a
result of awareness created by these documents and other influences [for example,
concern about the threat of bioterrorism (6)], Congress
appropriated funds to improve the public health infrastructure to address EID
threats, including funding for improving food safety and preparing for
bioterrorism. The public health community is using these funds to strengthen
the critical functions of detecting, controlling, and preventing infectious diseases. Maximizing the benefits from
these resources will require balancing the need to replenish basic capacity
depleted during years of inadequate funding (1) with the
need to incorporate new technologies and plan for the longer term.
Detection of EIDs
Rapid detection of EIDs is essential to minimize illness, disability, death, and
economic losses. Public health surveillance--the ongoing, systematic
collection, analysis, interpretation, and dissemination of health data--is the
cornerstone of problem detection and response. The usefulness of augmenting
routine surveillance with new technologies--such as molecular tools and rapid
communications methods--has been demonstrated many times. For example, the
National Molecular Subtyping Network for Foodborne Disease Surveillance (7) (also known as PulseNet; Fig. 1) has contributed
to the identification of several multistate outbreaks with relatively few
affected persons in any given place (8). When intensive laboratory
study of an illness with characteristics that suggest an infectious origin
fails to identify a causative agent, creative approaches, such as searching for
host mRNA response profiles that are agent- or class-specific (9),
may help solve the puzzle.
National Molecular Subtyping Network for Foodborne Disease Surveillance (PulseNet) (7). PulseNet is a molecular subtyping network conducted by the Centers for
Disease Control and Prevention (CDC), state health departments, the U.S. Department of
Agriculture (USDA), the Food and Drug Administration (FDA), and the Association of Public
Health Laboratories. Participating clinical and public health laboratories electronically
submit pulsed field gel electrophoresis (PFGE) images from clinical specimens to a
database, and within minutes the CDC-based computer returns information on specimens with
similar PFGE patterns. USDA and FDA laboratories submit PFGE images on isolates from food
items to the system. [View Larger
Version of this Image (38K GIF file)]
Although laboratory testing has been the basis for identifying many new diseases, clinicians are often the first to
recognize a new disease problem. Networks of medical specialists in emergency
medicine, infectious diseases, and
travel medicine have been formed recently to enhance collaboration about EIDs (10). Physicians in these networks systematically collect data
about difficult infectious disease problems, as well as use the Internet and
other means to rapidly circulate queries about diagnosis and management of
uncommon or poorly understood infectious illnesses. These capacities could be
potentially useful during an influenza pandemic or certain bioterrorist events.
Control of EIDs
Systems for detecting infectious disease problems must be tightly linked to systems for
controlling them. In addition to ensuring adequate capacity for routine public
health control functions, we must ensure surge capacity--ways of rapidly
increasing laboratory, epidemiologic, and other staff and facilities to test
specimens, conduct epidemiologic investigations, and otherwise respond to difficult
and complex public health problems. Additionally, special capacities must be
available to address problems that are not part of routine public health--for
example, to test for organisms that require Biosafety Level 4 facilities
(known lethal organisms potentially transmissible in a laboratory environment
for which no known prophylaxis or treatment is available) or to manufacture
and distribute vaccines and medications during an influenza pandemic.
Prevention of EIDs
Preventing EIDs requires using proven tools, and developing and evaluating new ones.
Vaccines provide excellent examples of proven, cost-effective disease
prevention. For instance, in 1993 in the United States, 23 million elderly
people failed to receive the pneumococcal vaccine; vaccination would have saved
an estimated 78,000 years of healthy life and $194 million (11). Other proven prevention tools include screening and
treatment of blood and blood products to prevent hepatitis B and HIV
transmission (12) and administering intrapartum antibiotics
to women at high risk for transmitting Group B Streptococcus to their
newborns (Fig. 2) (13).
Association between hospital policies and rates of Group B streptococcal (GBS) disease,
1996. As much as 41 to 78% of GBS disease in the first week of life can be
prevented by appropriate use of antibiotics. According to 1996 data from sites with
intensive surveillance for invasive GBS disease in seven states, geographic areas in which
a higher proportion of hospitals had GBS perinatal disease prevention policies had lower
incidences of early-onset GBS disease (R2 = 0.62, P = 0.03)
(13). [View Larger
Version of this Image (11K GIF file)]
For some disease problems, such as antimicrobial resistance, effective approaches to
prevention and control have been difficult to develop and implement (14). Overuse and misuse of antimicrobial agents are major
contributors to antimicrobial resistance. Reducing inappropriate prescribing of
antimicrobial agents requires intensive, sustained efforts; approaches that
have been used with varying success have included physician and patient
education, peer review with feedback, computer-assisted decision support, and
administrative interventions (15). Examples of newer
approaches that will place less emphasis on behavior change (16)
include targeting bacterial virulence (which would not lead to selective
pressure for antimicrobial resistance) (17) and changing
food production practices (18), for example, the use of
competitive exclusion (selectively establishing indigenous intestinal flora in
food animals to reduce colonization with pathogenic or resistant organisms) (19). Development of new vaccines that reduce the number of
people asymptomatically harboring an organism [for example, the soon-to-be
licensed pneumococcal conjugate vaccine for young children (20)]
may decrease antimicrobial resistance by interrupting transmission of the
target organism, with resultant reductions in antibiotics used for treating
actual disease or presumptive treatment of other conditions.
Long-term Challenges for the Public Health Response to EIDs
Most of the factors that contribute to disease emergence will continue, if not
intensify, in the 21st century (3). These include social
factors (for example, lack of adequate health care and increases in
international travel), demographic factors (for example, the aging of the
population in developed countries, urbanization, and population growth), and
environmental factors (for example, global climate change, lack of adequate
sanitation, and land use practices that result in human contact with previously
remote habitats), as well as microbial evolution. The public health community
must develop long-term strategies to respond to these challenges.
As we enter the new millennium, new technologies, like biosensors (21)
and high-density DNA microarrays (22), are likely to have
profound effects on clinical medicine and public health practice. Biosensors
use immobilized antibodies or antigens to detect minute concentrations of their
binding partners in biologic fluids. Microarrays consist of arrangements of
thousands of sequences of synthetic or cloned DNA sequences able to detect
complementary sequences in a sample. These techniques may allow rapid and
specific disease diagnosis, so that a clinician can rapidly determine what
organism is causing an illness and whether it carries antimicrobial resistance
New understandings of human genetics may lead to immunizations, treatments, and other
interventions tailored to an individual's genetic profile (23);
the public health community must help develop, assess, and use genetic tests (24). New informatics tools to link and analyze large, diverse,
and distributed databases will facilitate important public health findings but
will raise difficult issues related to patient privacy (25).
The sheer volume of data available for analysis, for example, on human
genetic profiles as analyzed on microarrays, will require new methods for
studying associations between the characteristics of individuals and their risk
for diseases and responsiveness to
treatments. A new generation of DNA vaccines and edible vaccines may be safer
and more effective than those currently in use (26). Such
vaccines may be easier to produce, store, and transport than conventional
vaccines, greatly simplifying delivery even to remote parts of the world and
raising the possibility of global elimination or eradication of many diseases that have been difficult to control.
With increasing international travel and global commerce, prevention and control of
EIDs must involve global efforts (5, 27),
including ensuring adequate supplies of safe food and drinking water, providing
immunizations, improving personal hygiene, and reducing inappropriate
antimicrobial use. The recent threat from H5N1 influenza in Hong Kong (28) illustrates the importance of international communication
and cooperation and the need for a global perspective.
The public health community also needs to work more actively with other sectors (such
as agriculture, economic development, and health care) with important roles and
interests in reducing infectious diseases.
In recent years, the decisions to slaughter cows potentially infected with
bovine spongiform encephalitis in Britain and to slaughter poultry to stop
influenza H5N1 infection in Hong Kong, and proposals to modify regulations
governing the use of antimicrobial agents in food production in the United
States and elsewhere are examples of multisector responses to EID threats.
Even greater collaboration will be necessary to deal with poverty, a
particularly recalcitrant contributor to and consequence of infectious diseases. For example, malaria has its greatest
impact among the poor nations of sub-Saharan Africa, where annually it kills
at least 430,000 to 680,000 children (29) and costs
1% of the 1995 gross national product in sub-Saharan Africa (30).
Infectious diseases are currently the
third leading cause of death in the United States (31) and the leading
cause worldwide (27). The potential threats to public
health from problems such as antimicrobial resistance and new infectious agents
will continue. We must make a long-term commitment now to ensure the capacity
to address current EID problems as well as those in the future.
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