EMERGING INFECTIOUS DISEASES

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CONTENTS, EMERGING INFECTIOUS DISEASES, VOL. 1, NO. 2

Perspective

Travel and the Emergence of Infectious Diseases, 
Mary E. Wilson

Synopsis

Escherichia coli Serotype O157:H7: Novel Vehicles of
Infection and Emergence of Phenotypic Variants,
 Peter Feng 

Dispatches

Epidemic-Associated Neisseria meningitidis Detected by
Multilocus Enzyme Electrophoresis, 
Michael W. Reeves, Bradley A. Perkins, and 
Jay D. Wenger

Dengue/Dengue Hemorrhagic Fever: The Emergence of a
Global Health Problem, 
Duane J. Gubler and Gary G. Clark

Progress Toward the Eradication of Dracunculiasis (Guinea
Worm Disease): 1994, 
Ernesto Ruiz-Tiben, Donald R. Hopkins, Trenton K. 
Ruebush, and Robert L. Kaiser

Letters

Heat-Stable Enterotoxin-Producing Escherichia coli
O169:H41 in Japan, 
Yoshikazu Nishikawa, Masaki Hanaoka, Jun Ogasawara, 
Nelson P. Moyer, and Teruo Kimura

The GAP Project in Southeastern Turkey: The Potential for
Emergence of Diseases, 
Serap Aksoy, Sedat Ariturk, Martine Y.X. Armstrong, K. P.
Chang, Zeynep Drtbudak, Michael Gottlieb, M. Ali Ozcel, 
Frank F. Richards, and Karl Western


Commentary

Action Plan for Drug-Resistant Streptococcus pneumoniae,
Martin S. Cetron, Daniel B. Jernigan, Robert F.
Breiman, and the DRSP Working Group

News and Notes 

WHONET: An Information System for Monitoring
Antimicrobial Resistance, 
Thomas F. O'Brien and John M. Stelling


Recommendations for Preventing the Spread of Vancomycin
Resistance, 
Hospital Infection Control Practices Advisory 
Committee

Waterborne Cryptosporidiosis Threat Addressed, 
Daniel G. Colley


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PERSPECTIVE

Travel and the Emergence of Infectious Diseases

Mary E. Wilson, M.D.

Harvard School of Public Health and Harvard Medical
School, Boston, Massachusetts, USA
Member: Harvard Working Group on New and Resurgent
Infectious Diseases

Abstract

Travel is a potent force in the emergence of disease.
Migration of humans has been the pathway for
disseminating infectious diseases throughout recorded
history and will continue to shape the emergence,
frequency, and spread of infections in geographic areas
and populations. The current volume, speed, and reach of
travel are unprecedented. The consequences of travel
extend beyond the traveler to the population visited and
the ecosystem. When they travel, humans carry their
genetic makeup, immunologic sequelae of past infections,
cultural preferences, customs, and behavioral patterns.
Microbes, animals, and other biologic life also accompany
them. Today's massive movement of humans and materials
sets the stage for mixing diverse genetic pools at rates
and in combinations previously unknown. Concomitant
changes in the environment, climate, technology, land
use, human behavior, and demographics converge to favor
the emergence of infectious diseases caused by a broad
range of organisms in humans, as well as in plants and
animals.

Many factors contribute to the emergence of infectious
diseases. Those frequently identified include microbial
adaptation and change, human demographics and behavior,
environmental changes, technology and economic
development, breakdown in public health measures and
surveillance, and international travel and commerce
(1-4). This paper will examine the pivotal role of global
travel and movement of biologic life in the emergence of
infectious diseases. It will also examine the ways in
which travel and movement are inextricably tied at
multiple levels to other processes that influence the
emergence of disease.

Travel is a potent force in disease emergence and spread
(5). The current volume, speed, and reach of travel are
unprecedented. The consequences of migration extend
beyond the traveler to the population visited and the
ecosystem (6). Travel and trade set the stage for mixing
diverse genetic pools at rates and in combinations
previously unknown. Massive movement and other
concomitant changes in social, political, climatic,
environmental, and technologic factors converge to favor
the emergence of infectious diseases.

Disease emergence is complex. Often several events must
occur simultaneously or sequentially for a disease to
emerge or reemerge (Table 1) (6). Travel allows a
potentially pathogenic microbe to be introduced into a
new geographic area; however, to be established and cause
disease a microbe must survive, proliferate, and find a
way to enter a susceptible host. Any analysis of
emergence must look at a dynamic process, a sequence of
events, a milieu, or ecosystem.

Movement, changing patterns of resistance and
vulnerability, and the emergence of infectious diseases
also affect plants, animals, and insect vectors. Analysis
of these species can hold important lessons about the
dynamics of human disease.

Table 1.  Basic concepts in disease emergence*
__________________________________________________________
Emergence of infectious diseases is complex.

Infectious diseases are dynamic.

Most new infections are not caused by genuinely new 
pathogens.

Agents involved in new and reemergent infections cross
taxonomic lines to include viruses, bacteria, fungi, 
protozoa, and helminths.

The concept of the microbe as the cause of disease is 
inadequate and incomplete.

Human activities are the most potent factors driving 
disease emergence.

Social, economic, political, climatic, technologic, and 
environmental factors shape disease patterns and influence
emergence.

Understanding and responding to disease emergence require 
a global perspective, conceptually and geographically.

The current global situation favors disease emergence.
__________________________________________________________
*Adapted from Wilson ME (6).


To assess the impact of travel on disease emergence, it
is necessary to consider the receptivity of a geographic
area and its population to microbial introduction. Most
introductions do not lead to disease. Organisms that
survive primarily or entirely in the human host and are
spread through sexual contact, droplet nuclei, and close
physical contact can be readily carried to any part of
the world. For example, AIDS, tuberculosis, measles,
pertussis, diphtheria, and hepatitis B are easily carried
by travelers and can spread in a new geographic area;
however, populations protected by vaccines resist
introduction. Organisms that have animal hosts,
environmental limitations, arthropod vectors, or
complicated life cycles become successively more
difficult to "transplant" to another geographic area or
population. Epidemics of dengue fever and yellow fever
cannot appear in a geographic area unless competent
mosquito vectors are present. Schistosomiasis cannot
spread in an environment unless a suitable snail
intermediate host exists in that region. Organisms that
survive only under carefully tuned local conditions are
less likely to be successfully introduced. Even if an
introduced parasite persists in a new geographic area, it
does not necessarily cause human disease. In the United
States, humans infected with Taenia solium, the parasite
that causes cysticercosis, infrequently transmit the
infection because sanitary disposal of feces, the source
of the eggs, is generally available. In short, the
likelihood of transmission involves many biological,
social, and environmental variables.

Historical Perspective 

Human migration has been the main source of epidemics
throughout recorded history. William McNeill (7), in his
book Plagues and Peoples, describes the central role of
infectious disease in the history of the world. Patterns
of disease circulation have influenced the outcome of
wars and have shaped the location, nature, and
development of human societies.

Trade caravans, religious pilgrimages, and military
maneuvers facilitated the spread of many diseases,
including plague and smallpox. A map in Donald Hopkins'
book, Princes and Peasants: Smallpox in History (8),
traces the presumed spread of smallpox from Egypt or
India, where it was first thought to have become adapted
to humans sometime before 1000 B.C. Smallpox spread
easily from person to person through close contact with
respiratory discharges and, less commonly, through
contact with skin lesions, linens, clothing, and other
material in direct contact with the patient. Because
patients remained infectious for about 3 weeks, many
opportunities for transmission were available. Even in
this century, until the 1970s, smallpox continued to
cause epidemics. A pilgrim returning from Mecca was the
source of a large outbreak in Yugoslavia in the early
1970s that resulted in 174 Yugoslav cases and 35 deaths
(9). The pilgrim apparently contracted the infection in
Baghdad while visiting a religious site. Because his
symptoms were mild, he was never confined to bed and was
able to continue his travels and return home.

For most of history, human populations were relatively
isolated. Only in recent centuries has there been
extensive contact between the flora and fauna of the Old
and New Worlds. Schoolchildren hear the rhyme "Columbus
sailed the ocean blue, in fourteen hundred ninety-two,"
but may learn little about the disaster brought upon the
native populations of the Americas by the arriving
explorers. By the end of the fifteenth century, measles,
influenza, mumps, smallpox, tuberculosis, and other
infections had become common in Europe. Explorers from
the crowded urban centers of Europe brought infectious
diseases to the New World (10), where isolated
populations had evolved from a relatively small gene pool
and had no previous experience with many infections (11).
The first epidemics following the arrival of Europeans
were often the most severe. By 1518 or 1519, smallpox
appeared in Santo Domingo, where it killed one-third to
half of the local population and spread to other areas of
the Caribbean and the Americas (10). The population of
central Mexico is estimated to have dropped by one-third
in the single decade following contact with the
Europeans.

Travel across the Atlantic Ocean transformed the flora
and fauna of the New World as well. Some of the
transported materials became important sources of food
(plants), clothing, and transportation (animals). Other
transfers were less welcome: Japanese beetles, Dutch elm
disease, and chestnut tree fungus. A.W. Crosby, exploring
these exchanges between the Old and the New Worlds,
sounds a pessimistic note: "The Columbian exchange has
left us with not a richer but a more impoverished genetic
pool" (10).

The explorers also paid a price in loss of lives from
disease. Philip Curtin (12) provides a quantitative study
of "relocation costs," the excess illness and death among
European soldiers in the nineteenth century when they
lived or worked in the tropics. Until the most recent
armed conflicts, infectious diseases claimed more lives
than injuries during wars.

Plague holds a prominent place in history and remains
with us today. A bacterial infection caused by Yersinia
pestis, it is primarily an infection of rodents, spread
by their fleas. Human infection is incidental to the
maintenance of Y. pestis in animal reservoirs. Yet plague
periodically has erupted in human populations, wreaking
great devastation, killing millions and causing infection
that can be spread directly from person to person by the
respiratory route. Human population movement has been
essential in the spread of plague and the dispersal of
rodents and their fleas to new areas. For centuries
plague spread along trade routes. It reached California
by boat around the turn of this century, caused epidemic
infection in San Francisco, and then spread to wildlife,
where it persists today in a large enzootic focus.

Movement of People

Travel for business and pleasure constitutes a small
fraction of total human movement (5,13). People migrating
individually or in groups, may be immigrants, refugees,
missionaries, merchant marines, students, temporary
workers, pilgrims, or Peace Corps workers. Travel may
involve short distances or the crossing of international
borders. Its volume, however, is huge. In the early 1990s
more than 500 million persons annually crossed
international borders on commercial airplane flights
(World Tourism Organization, Madrid, unpublished data).
An estimated 70 million persons, mostly from developing
countries, work either legally or illegally in other
countries (14). Movement may be temporary or seasonal, as
with nomadic populations and migrant workers who follow
the crops. Military maneuvers worldwide employ and move
huge populations. The consequences of armed conflict and
political unrest displace millions. In the early 1990s,
there were an estimated 20 million refugees and 30
million displaced persons worldwide (International
Organization for Migration, personal communication).

Grubler and Nakicenovic estimated and plotted the average
kilometers traveled daily for the French population over
a 200-year period (1800-2000) and found that spatial
mobility has increased more than 1000-fold (15). In the
last 40 years, the size of Australia's population has
doubled and the number of persons moving into and out of
Australia has increased nearly 100-fold (16).

Although social, economic, and political factors push
people from an area or draw them to another,
environmental resources and their impact on food and
water supplies are behind many conflicts leading to
displacement of populations. Acute disasters, such as
flooding, earthquakes, and hurricanes often force
populations to seek shelter and sustenance in new lands.
Chronic changes, such as drought, depletion of soil, and
disappearance of fish from streams, lakes, and oceans,
draw people to new territories, or, more frequently, to
the fringes of large urban centers.

Another type of travel relevant to disease emergence is
the shift of populations to urban areas. It is estimated
that by the year 2010, 50% of the world's population will
be living in urban areas. It is projected that by the
year 2000, the world will comprise 24 "megacities" 
sprawling metropolitan areas with populations exceeding
10 million (World Bank, UNDP, World Health Organization,
 unpublished data). These areas will have the population
density to support persistence of some infections and 
contribute to the emergence of others. Many of these 
areas are located in tropical or subtropical regions, 
where the environment can support a diverse array of 
pathogens and vectors. Also developing are huge 
periurban slums, populated with persons from
many geographic origins. Poor sanitation allows breeding
of arthropod vectors, rodents, and other disease-carrying
animals. Crowded conditions favor the spread of diseases
that pass from person to person, including sexually
transmitted infections. Travel between periurban slum
areas and rural areas is common, paving the route for the
transfer of microbes and disease. Transfer of resistance
genes and genetic recombination may also occur in and
spread from crowded environments of transients.

Acute disturbances, whether climatic or political, lead
to interim living arrangements, such as refugee camps and
temporary shelters, that provide ideal conditions for the
emergence and spread of infections. Temporary living
quarters often share similarities with periurban slums:
crowding, inadequate sanitation, limited access to
medical care, lack of clean water and food, dislocation,
multiethnic composition, and inadequate barriers from
vectors and animals. An example is the movement of
500,000-800,000 Rwandan refugees into Zaire in 1994.
Almost 50,000 refugees died during the first month as
epidemics of cholera and Shigella dysenteriae type 1
swept through the refugee camps (17).

Movement into a rural environment poses different risks
and often places new rural populations in contact with
pathogens that are in the soil and water or are carried
by animals or arthropods (18). Some of these pathogens
such as Guanarito (19) and Sabi  viruses (20) in South
America, were only recently recognized as capable of
infecting humans.

Consequences of Movement 

Human migration favors the emergence of infectious
diseases through many mechanisms. When people migrate,
they carry their genetic makeup, their accumulated
immunologic experience, and much more (Table 2). They may
carry pathogens in or on their bodies and may also
transport disease vectors, such as lice. Their technology
(agricultural and industrial), methods for treating
disease, cultural traditions, and behavioral patterns may
influence their risk for infection in a new environment
and their capacity to introduce disease into the new
region. Their social standing and resources may affect
their exposure to local infections and their access to
adequate nutrition and treatment. People also change the
environment in many ways when they travel or migrate--they
plant, clear land, build, and consume. Travel is relevant
in the emergence of disease if it changes an ecosystem.
The following examples show the many ways in which
migration can influence the emergence of disease in a new
area.

Table 2.  What is carried by humans into new regions?
__________________________________________________________
Pathogens in or on body

Microbiologic flora

Vectors on body

Immunologic sequelae of past infections

Vulnerability to infections

Genetic makeup

Cultural preferences, customs, behavioral patterns,
technology

Luggage and whatever it contains
__________________________________________________________


1. Humans may carry a pathogen in a form that can be
transmitted, then or later, directly or indirectly to
another person. The pathogen may be silent (during the
incubation period, chronic carriage, or latent infection)
or clinically evident. Examples include hepatitis B
virus, human immunodeficiency virus (HIV), Mycobacterium
tuberculosis, M. leprae, Salmonella typhi, and other
salmonella. Disease may be especially severe when a
pathogen is introduced into a population that has no
previous exposure to the infection. How long the
consequences of migration persist varies with the
specific infection. The two most critical characteristics
are the duration of survival of the pathogen in a
potentially infective form and its means of transmission.

2. Epidemic cholera in Africa spread along the West
African coast and, when the disease moved inland,
followed fishing and trading routes. Markets, funerals,
refugee camps--events that involved migration of persons
and large gatherings with close contact--helped spread the
infection. With El Tor cholera, asymptomatic and mild
infections can outnumber severe disease by 100 to 1 (21),
thus permitting those infected to continue to move and
work.

3. Pilgrims carried an epidemic strain of group A
Neisseria meningitidis from southern Asia to Mecca in
1987. Other pilgrims who became colonized with the
epidemic strain introduced it into sub-Saharan Africa,
where it caused a wave of epidemics in 1988 and 1989
(22).

4. Humans may carry a pathogen that can be transmitted
only if conditions are permissive. This permissiveness
can pertain to human behavior, the environment, or the
presence of appropriate vectors or intermediate hosts.
For example, the ease with which HIV spreads in a
population depends on sexual practices, condom use, the
number of sex partners, and intravenous drug use, among
other factors. Malaria requires specific mosquito vectors
(with access to susceptible humans) to spread to new
geographic regions. Schistosomiasis can be introduced
into a new region only if the appropriate snail host is
present and if the eggs excreted (in urine or feces, from
an infected person), reach the snails in an appropriate
environment.

5. Humans may carry a strain of microbe that has an
unusual resistance pattern or virulence genes. A
multiple-drug-resistant strain of Klebsiella pneumoniae
appears to have been transferred by an asymptomatic woman
from a hospital in Bahrain to Oxford, where it caused
outbreaks in two British hospitals (23). People also
carry their background flora, in the intestinal tract,
for example, which may contain plasmids and resistance
genes that can interact with microbes in a new area. It
is not just the classic pathogens that may be relevant to
the emergence of a new disease but the individual
traveler's total microbiologic "baggage."

6. Visitors to a region may lack immunity to locally
endemic infections, such as hepatitis A and sand-fly
fever. Visitors may suffer severe or different
manifestations of infection or disease at an age when the
local population is immune to it. Resettlement of
populations into malaria-endemic regions can lead to a
high death rate from falciparum malaria.

7. Kala-azar caused a deadly outbreak in remote villages
in southern Sudan in 1994. The origin was thought to be
the villagers' exposure to the sand-fly vector during
migration to a food distribution center that had been
established by a relief organization (24). The migration
took a malnourished population from a nonendemic zone
into the southern part of the kala-azar endemic zone.
Unfamiliarity with the disease and the poor nutritional
status of the population probably contributed to a high
death rate (24).

8. Behavioral patterns in a new region may place visitors
at risk for infection, while the local population,
possibly because of their knowledge of disease risks, may
not be at risk. Behavior patterns may involve food
preparation (such as eating some foods raw), clothing (or
lack of it) (for example, going barefooted), sleeping
arrangements (sleeping on the ground or out of doors in
an unscreened area), and contact with animals.

9. Susceptibility of a population may vary because of
genetic differences. A microbe introduced into a new
region may have a greater or lesser impact, depending on
the host population. Genetic factors influence
susceptibility to and expression of several infectious
diseases. Although these interactions are not yet well
defined for most infections, genetic factors influence
infections caused by different classes of organisms,
including cholera (25,26), parvovirus infection (27),
malaria, and Helicobacter pylori infection (28).

To determine the consequences of travel both the traveler
and the population visited must be considered. Migration
may be in only one direction, though travel often
involves returning to the point of origin, perhaps after
the traveler has made many stops along the way. The
changes in the various ecosystems as a consequence of the
migration guide the emergence of diseases; any study that
simply focuses on the traveler is too narrow.

The distance traversed is less important than the
differences in biological life in different areas and
differences in receptivity and vulnerability. In thinking
about disease emergence, what matters is the potential of
a disease to appear in a place, population, or extent not
previously reported.

What is the long-term impact of migration and travel on
human disease? Carriage of pathogens is only part of the
influence on disease emergence. Introduced technology,
farming methods, treatment and drugs, chemicals, and
pesticides may have a far greater and longer impact on
disease patterns in a region than the life of a person.
Deforestation, building of dams, and opening of roads
into previously inaccessible areas have all been
associated with population movements and changes in
distribution and frequency of a variety of infections in
humans (such as malaria, schistosomiasis, Rift Valley
fever, and sexually transmitted diseases).

Increasingly the vehicle of transportation is the site or
even the source of outbreaks. During travel, people from
diverse origins are enclosed in close proximity for a
hours or days and then discharged to move on to many
distant places. These temporary new habitats, jumbo jets
or huge ocean liners, can be the sites for dissemination
of the microbes (as happens, for example with Legionella
pneumophila infections (29), foodborne infections, and
cholera) or provide a milieu for person-to-person
transmission (influenza, tuberculosis (30,31)).

Shipping and Commerce

The biomass of humans constitutes only a fraction of the
matter moved about the earth. Humans carry and send a
huge volume of plants, animals and other materials all
over the face of the globe. Much of this movement results
from the planned transport of goods from one place to
another, but some is an unintended consequence of
shipping and travel. All has an impact on the
juxtaposition of various species in different ecosystems.
"Hitchhikers" include all manner of biologic life, both
microscopic and macroscopic. Animals can carry potential
human pathogens and vectors. The globalization of markets
brings fresh fruits and vegetables to dinner tables
thousands of miles from where they were grown,
fertilized, and picked. Tunnels, bridges, and ferries
form means to traverse natural barriers to species
spread. The roads built to transport people often speed
the movement of diseases from one area to another. Mass
processing and wide distribution networks allow for the
amplification and wide dissemination of potential human
microbes.

Examples of introduced species include plants and
animals--insects, microbes, and marine organisms.

1. Ships convey marine organisms on their hulls and in
their ballast water. For example, 367 different species
were identified in ballast water of ships traveling
between Japan and Coos Bay, Oregon (32). Introductions
have had devastating effects in some areas, for example
such as the Black and Azov seas, where newly introduced
jellyfish-like creatures called ctenophores have ruined
local fishing (33).

2. Vibrio cholerae may have been introduced to South
America by shipping (34). Researchers isolated the
organism in samples of ballast, bilge, and sewage from 3
of 14 cargo ships docked at Gulf of Mexico ports. The
ships had last ports of call in Brazil, Colombia, and
Chile (35). V. cholerae O1, serotype Inaba, biotype El
Tor, indistinguishable from the Latin American epidemic
strain, was found in oysters and oyster-eating fish from
closed oyster beds in Mobile Bay, Alabama (36). V.
cholerae O139 has spread along waterways in Asia,
although the people carried on the boats doubtless played
a role (37,38).

3. Aedes albopictus was introduced into the United States
inside used tires shipped from Asia (39,40). The
mosquito's introduction causes concern because it is an
aggressive biter, survives in both forest and suburban
habitats, and appears to be a competent vector for
several human pathogens. It has been associated with
epidemic dengue fever transmission in Asia and is a
competent laboratory vector of La Crosse, yellow fever,
and other viruses (41). In Florida, 14 strains of eastern
equine encephalitis virus have been isolated from A.
albopictus (42). The mosquito is now established in at
least 21 of the contiguous states in United States and in
Hawaii.

4. The African anopheles mosquitoes arrived in Brazil in
about 1929. This vector could breed under conditions
other New World mosquitoes could not. Although the
malaria parasite was already found in Brazil, this new
vector expanded the range of transmission. An estimated
20,000 persons died of malaria before the introduced
anopheles mosquitoes were eliminated.

5. It has been repeatedly demonstrated that mosquitoes are
present--and--survive on international flights. In random
searches of airplanes in London, mosquitoes were found on
12 of 67 airplanes from tropical countries (43).
Arthropods can survive even more extreme environments. In
one study, mosquitoes, house flies, and beetles placed in
wheel bays of Boeing 747B aircraft survived flights of
6-9 hours with external temperatures of -42  C (43).
Airplanes have also carried infective mosquitoes that
caused human infection outside malaria-endemic areas (in
Europe, for example).

6. Vehicles can transport vectors over land. Glossina
palpalis, a vector for African trypanosomiasis (sleeping
sickness), can fly up to 21 km but can be transported
much longer distances on animals and in land vehicles.

7. Seven persons in Marburg, Germany, died after handling
blood and tissues from African green monkeys from Uganda.
The tissues contained an organism later named Marburg
virus (44).

8. Exotic animals transported from their usual habitats
are clustered in zoos; others are used in research
laboratories where they have occasionally caused severe
disease in humans. Two examples are B virus from primates
(45) and hemorrhagic fever with renal syndrome from
rodents (46).

9. The world trade and globalization of organs, tissues,
blood, and blood products is growing. Researchers are
considering animals as sources for tissues and organs for
transplantation (47).

10. Plants may not directly cause human disease. But they
can alter an ecosystem and facilitate the breeding of a
vector for human disease. This can also displace
traditional crops that provide essential nutrition.
Vertical transmission of plant pathogens (and spread of
plant diseases) can result from seed movement (48).
Carriage of seeds into new areas can introduce plant
pathogens.
11.Migration and altered environments have increased the
so-called weedy species. These species migrate easily and
have high rates of reproduction. If they lack local
predators, they can displace other species and often
upset local ecology.

Introduction of Species into New Areas

Introducing species into new geographic areas is not new,
but the current volume and frequency of introductions are
unprecedented. A pathogen's survival and spread in a new
environment are determined by its basic reproductive
rate, which is the average number of successful offspring
a parasite can produce (49). To invade and establish
itself in a host population, a parasitic species must
have a basic reproductive rate exceeding one (49). The
simplicity of this statement belies the complexity of
circumstances that influence invasion and persistence.
These circumstances encompass biological, social, and
environmental factors.

As noted already, factors that can influence receptivity
include climate and environmental conditions, sanitation,
socioeconomic conditions (50), behavior, nutrition, and
genetics. V. cholerae persists in an aquatic reservoir
off the Gulf Coast of the United States, yet epidemic
cholera has not been a problem in the United States.
Where poverty and poor sanitation prevail, the presence
of V. cholerae can be a source of endemic disease and
periodic epidemics.

Disease emergence is often complex. An outbreak of
malaria in San Diego, California, occurred when
parasitemic migrant workers were employed in an area
where mosquitoes capable of transmitting malaria had
access to the workers and to a susceptible human
population (51). Many conditions had to be met to allow
transmission.

Migration may introduce parasites into an area where a
different intermediate host or vector could change the
incidence of disease. Cycling through a different host
can lead to different transmission rates, different
infectivity, and even different clinical expression. A
parasite may be more successful in a new site because of
a larger susceptible population or the absence of
predators.



Confluence of Events

Massive global travel is taking place simultaneously with
many other processes that favor the emergence of disease.
For example, the human population is more vulnerable
because of aging, immunosuppression from medical
treatment and disease (such as AIDS), the presence of
prostheses (e.g., artificial heart valves and joints),
exposure to chemicals and environmental pollutants that
may act synergistically with microbes to increase the
risk of diseases, increased poverty, crowding and stress,
and increased exposure to UV radiation. Technologic
changes, while providing many benefits, can also promote
disease dissemination. Resistance of microbes and insects
to antimicrobial drugs and pesticides interferes with the
control of infections and allows transmission to
continue. Changes in land use can alter the presence and
abundance of vectors and intermediate hosts.

Microbes are enormously resilient and adaptable. They
have short life spans, which allow rapid genetic change.
Humans, by comparison, are slow to change genetically but
can change their behavior. People move and construct
barriers to prevent contact with microparasites,
macroparasites, and the extremes of the environment.
Technology fosters a perception of human invincibility
but actually creates new vulnerabilities, as it enables
us to go deeper, higher, and into more remote and hostile
environments. Studies show that no place on earth is
devoid of microbes. Their range and resiliency are truly
phenomenal. Only a fraction of the existing microbes have
been characterized. Travel and exploration provide a
greater opportunity for humans to come into unsampled
regions with these uncharacterized microbes. 

Summary and Conclusions

Global travel and the evolution of microbes will
continue. New infections will continue to emerge, and
known infections will change in distribution, severity
and frequency. Travel will continue to be a potent factor
in disease emergence. The current world circumstances
juxtapose people, parasites, plants, animals, and
chemicals in a way that precludes timely adaptation. The
combination of movement at many levels and profound
change in the physical environment can lead to
unanticipated diseases spread by multiple channels. In
many instances, the use of containment or quarantine is
not feasible. Research and surveillance can map the
global movement and evolution of microbes and guide
interventions. Integration of knowledge and skills from
many disciplines--the social, biological, and physical
sciences--is needed. The focus should be system analysis
and the ecosystem rather than a disease, microbe, or
host.

Dr. Wilson is Chief of Infectious Diseases at Mount
Auburn Hospital in Cambridge and Assistant Professor of
Population and International Health and Epidemiology at
the Harvard School of Public Health. An active
participant in the Harvard Working Group on New and
Reemergent Infectious Diseases since its inception in
1991, she is the senior editor, with Richard Levins and
Andrew Spielman, of Disease in Evolution: Global Changes
and Emergence of Infectious Diseases (3), a book based on
the 1993 Woods Hole workshop on emerging infections.


Address for correspondence:  Mary E. Wilson, Division
of Infectious Diseases, Mt. Auburn Hospital, 330 Mt. 
Auburn Street, Cambridge, MA  02238 USA, fax 
617-965-6632; e-mail mewilson@warren.med.harvard.edu


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SYNOPSIS

Escherichia coli Serotype O157:H7: Novel Vehicles of
Infection and Emergence of Phenotypic Variants

Peter Feng, Ph.D.
U.S. Food and Drug Administration, Washington, D.C., USA


Abstract

Escherichia coli serotype O157:H7 was only recognized as
a human pathogen a little more than a decade ago, yet it
has become a major foodborne pathogen. In the United
States, the severity of serotype O157:H7 infections in
the young and the elderly has had a tremendous impact on
human health, the food industry, and federal regulations
regarding food safety. The implication of acidic foods as
vehicles of infection has dispelled the concept that
low-pH foods are safe. Further, the association of
nonbovine products with outbreaks suggests that other
vehicles of transmission may exist for this pathogen. In
laboratory diagnosis, most microbiologic assays rely on
a single phenotype to selectively isolate this pathogen.
However, the increasing evidence that phenotypic
variations exist among isolates in this serogroup may
eventually necessitate modifications in assay procedures
to detect them.

Enterohemorrhagic Escherichia coli (EHEC) has emerged in
recent years as the predominant cause of hemorrhagic
colitis in humans. This illness, with characteristic
symptoms of bloody diarrhea and abdominal cramps, can
progress into a more severe, life-threatening
complication known as hemolytic uremic syndrome (HUS).
The pathogenicity of EHEC appears to be associated with
a number of virulence factors, including the production
of several cytotoxins (1,2). These toxins are
collectively referred to as verotoxins or Shiga-like
toxins (SLTs) because the SLT-I of E. coli closely
resembles the Shiga toxin of Shigella dysenteriae type 1
(2). Although more than 60 E. coli serotypes produce SLTs
(2) and more are being identified as capable of producing
SLT, serotype O157:H7 is the predominant pathogen in the
EHEC group and the one associated most frequently with
human infections worldwide.

Isolates of the serotype O157:H7 were first implicated in
foodborne illness in 1982; in the subsequent 10 years,
approximately 30 outbreaks were recorded in the United
States (1). In early 1993, however, serotype O157:H7
received considerable attention after a large foodborne
disease outbreak, traced to the consumption of
undercooked, contaminated hamburgers served at a regional
fast-food restaurant (3). More than 700 persons in four
states were infected; there were 51 cases of HUS and four
deaths. Since that outbreak, the reported incidence of
serotype O157:H7 infections has risen, partly because
better surveillance systems have been implemented and
awareness has increased among physicians, clinical
microbiologists, and consumers.  Fifteen additional
outbreaks were recorded in 1993 and 20 in the first half
of 1994.

Because serotype O157:H7 has only recently been
recognized as a foodborne pathogen, our knowledge is
limited. However, the notoriety of recent outbreaks and
the severity of serotype O157:H7 infections have
stimulated research on the organism, its ecology,
antibiotic resistance properties, and virulence factors.
Much has already been learned from the epidemiologic
investigations of past outbreaks.  For instance,
foodborne infections of serotype O157:H7 have most often
been associated with the consumption of bovine products;
however, several recent outbreaks have implicated other
less likely vehicles of infection and showed that the
organism may have some unsuspected characteristics.
Although genotypic studies show serotype O157:H7 to be a
unique clone only distantly related to other E. coli
serotypes (4,5), phenotypic diversity within the
serogroup (6) may complicate existing laboratory
diagnosis procedures. The introduction of various
molecular diagnostic techniques may facilitate the
detection of this serotype and its phenotypic variants.

This review examines unexpected and seemingly unlikely
vehicles implicated in recent serotype O157:H7 outbreaks
and the impact of emerging phenotypic variants and their
effect on diagnostic assays used to detect this pathogen
in clinical specimens or in the food supply.

Novel Vehicles of Transmission

So far, serotype O157:H7 has caused a total of  60
outbreaks of foodborne illness in the United States.
Consumption of contaminated, undercooked ground-beef
products has accounted for most outbreaks; however, raw
milk was also implicated in several outbreaks in the
United States and Canada.  Improper hygiene with
secondary spread from person-to-person contact is another
well-documented route of infection (1,2). In the last few
years, however, several foodborne outbreaks of serotype
O157:H7 have implicated unique and seemingly unlikely
vehicles of infection: among them are acidic foods,
fruits, salad vegetables, yogurt, and water.

Acidic foods

In the Retail Food Store Sanitation Code of the U.S. Food
and Drug Administration, foods with a pH value of less
than 4.6 are generally regarded as low risk in terms of
food safety. However, several recent disease outbreaks
attributable to serotype O157:H7 have shown that this
pathogen can persist in foods with low pH.

In the fall of 1991, an outbreak of serotype O157:H7 that
affected 23 persons was traced to the consumption of
fresh-pressed apple cider (7). The implicated cider, made
from unwashed "dropped" apples at a farm, had a pH value
of 3.7 to 3.9, was not pasteurized, and contained no
preservatives.  Although apple cider had been implicated
in a previous outbreak of Salmonella typhimurium, it is
not a common vehicle of enteric infection because of its
high acidity. Several laboratory studies have
subsequently demonstrated that isolates of serotype
O157:H7 can tolerate acidic conditions. Some strains
persist in media with pH values as low as 2.0 (8), and in
cold (8 C) apple cider for 10 to 31 days (7,9). Although
the source of serotype O157:H7 in the cider that caused
illness was never fully established, it was suspected
that the dropped apples had been contaminated by cow
manure. 

The ability of serotype O157:H7 to tolerate acidity was
substantiated in 1993, when another acidic food was
implicated in a series of restaurant outbreaks that
infected at least 48 persons. Although the source of the
outbreaks was not conclusively identified, epidemiologic
investigations and other data implicated mayonnaise or
mayonnaise-based dressing and sauces. Samples of
mayonnaise had a pH of 3.6 to 3.9, and the sauces
prepared from it were also acidic, with pH levels of 3.6
to 4.4 (10). After this outbreak, several studies
confirmed that although isolates of serotype O157:H7 do
not multiply under these conditions, they can persist in
commercial mayonnaise up to 55 days at 5 C (10,11). How
the mayonnaise became contaminated with serotype O157:H7
was not determined; however, improper handling of bulk
mayonnaise or cross-contamination with meat juices or
meat products was suspected.

Water

Several recent incidents show that both drinking water
and recreational water can serve as vehicles for
transmitting serotype O157:H7 infections.

The first and largest waterborne outbreak associated with
this pathogen occurred in Missouri in 1989 (12). Of the
more than 240 people infected, 32 were hospitalized, and
four died. The source of the outbreak was not identified,
but backflow during a water main break might have
contaminated the drinking water supply (12). Like most E.
coli, serotype O157:H7 isolates are susceptible to the
effects of chlorine. Hence, adjustments in the
chlorination of the drinking water supply during repairs
to the water main might have prevented the outbreak (12).

An outbreak caused by serotype O157:H7 and S. sonnei in
1991 may have involved recreational lake water in the
vicinity of Portland, Oregon. Of the 59 people affected,
21 (all children) were infected by serotype O157:H7 (13).
An epidemiologic survey showed that those who became ill
had swum in the lake during the previous 3-week period.
Transmission probably occurred when the swimmers
swallowed lake water that was fecally contaminated by
other bathers. The lengthy period during which people
became infected suggests that these pathogens can remain
viable in water for a long time, or that the water was
repeatedly recontaminated. Fecal contamination of
recreational water by bathers, especially small children,
is not uncommon; however, the contaminants are usually
diluted quickly by the large volume of water in
recreational lakes, bays, or rivers. That swallowing a
small amount of lake water can cause illness suggests
that the pathogen has a low infectious dose (13). This
fact is already well established for Shigella and seems
to be consistent with recent epidemiologic data from
foodborne outbreaks associated with serotype O157:H7.

A similar incident, implicating water from a children's
paddling pool, was reported in Scotland in 1992 (14).
Although epidemiologic evidence was not conclusive, the
available data suggested that a child with diarrhea had
played in the pool and fecally contaminated the water
with serotype O157. Because the pool water was not
changed or disinfected, it became the vehicle of
infection for two other neighborhood children, who in
turn infected others by person-to-person contact.

Other vehicles of transmission

Recently, several other unique vehicles have been
implicated in foodborne outbreaks associated with
serotype O157:H7. A 1993 outbreak in an Oregon restaurant
was apparently caused by the consumption of cantaloupe or
other items from the salad bar, which were most likely
cross-contaminated by meat products during preparation.
One study showed that serotype O157:H7 can survive and
grow on salad vegetables stored at 12 C and 21 C for up
to 14 days (15). An outbreak in the United Kingdom in
1991 was traced to the consumption of yogurt, which
infected 16 persons, 11 of them children (16). Although
consumption of raw milk has caused past outbreaks,
serotype O157:H7 is susceptible to heat treatment and
thus does not usually survive the pasteurization process.
Even though the implicated yogurt was prepared from
pasteurized milk, the milk might have become contaminated
with serotype O157:H7 after pasteurization.

A puzzling incident was reported from northern Italy,
where 15 cases of HUS, caused by serotype O157 and other
EHEC serotypes, was recorded over a 5-month period in
1993 (17). These cases occurred in small towns scattered
over a large area with little apparent connection to each
other; therefore, common food vehicles and exposure to
cattle were eliminated as possible sources of infection.
However, data from the epidemiologic investigations
suggested that contact with live poultry or with chicken
coops may have been the source of infection, even though
no toxin-producing EHEC strains were isolated from
poultry feces. A recent study showed that inoculating
1-day-old chicks with strains of serotype O157:H7
resulted in rapid colonization of the cecal tissue of the
chicks. The chicks then became long-term (up to 11
months) shedders of serotype O157:H7, and this
microorganism was subsequently recovered from the shells
of their eggs (18). It is conceivable, therefore, that
live poultry were the source of infection in the
outbreaks reported from northern Italy.

In December 1994, dry cured salami was implicated as the
source of serotype O157:H7 in a disease outbreak in the
state of Washington (19). A prior study showed that
although isolates of serotype O157:H7 do not grow in
seeded sausage batter, they can tolerate the acidity
produced during sausage fermentation and survive the
drying and the cold storage associated with the
preparation of dry sausages (20). Fermented sausages can
attain a pH as low as 4.8 (20). The ability of serotype
O157:H7 isolates to persist under these conditions is
consistent with the acid-tolerant properties this
organism exhibited in the previously discussed studies
with apple cider (7) and mayonnaise (10).

Although the consumption of bovine products still
accounts for most of the serotype O157:H7 infections, the
incidents described above show that other food types can
also serve as vehicles in transmitting infections with
this serotype.

Emergence of Phenotypic Variants 

Multilocus enzyme electrophoresis of E. coli strains
associated with enteric disease show that serotype
O157:H7 is in a well-defined group only distantly related
to other SLT-producing serotypes (4,5). Recently,
however, several phenotypic variants of this serotype
were isolated in Europe. Thus, in addition to causing
infections through food vehicles, the problems associated
with serotype O157:H7 are compounded by the emergence of
phenotypic variants, which may have an impact on
diagnostic assays used to detect this pathogen.

The clonal nature of serotype O157:H7 has facilitated its
phenotypic identification. Unlike other E. coli, isolates
of serotype O157:H7 do not ferment sorbitol in 24 hours
(21) and are negative in the methyl-umbelliferyl
glucuronide assay (22), which measures glucuronidase
activity (23). These phenotypes, especially the absence
of sorbitol fermentation, are used extensively to
distinguish isolates of serotype O157:H7 from related
bacteria. Isolation of serotype O157:H7 from foods, on
selective media, such as hemorrhagic colitis agar (24)
and cefixime-tellurite sorbitol-MacConkey agar (25) is
based on the sorbitol phenotype. Similarly,
sorbitol-MacConkey agar (26) is used in the clinical
laboratory as the primary screening medium to analyze
patient specimens for the presence of serotype O157:H7. 
Prompt culturing of bloody stools with this agar has been
very effective in isolating serotype O157:H7 from stool
specimens (1).

Although extremely useful, isolating and identifying the
pathogen exclusively on the absence of sorbitol
fermentation has some limitations. Other enteric
bacteria, such as E. hermanii and Hafnia spp., share
similar phenotypes and resemble serotype O157:H7 on
sorbitol-containing medium. Likewise, strains of O157, of
non-H7 serotype that are not pathogenic and do not
ferment sorbitol have occasionally been isolated from
foods (27). Because of the presence of phenotypically
similar species sorbitol negative isolates must be
serologically confirmed with O157 and H7 antisera (28).

Though intended solely to select for serotype O157:H7,
sorbitol-containing media may also exclude the isolation
of other pathogenic E. coli serotypes, many of which
ferment sorbitol. It appears that serotype O157:H7 is the
predominant pathogenic serotype worldwide; however, a
large number of other serotypes also produce SLT (1,2).
Although many of these have not been implicated in
disease or are known to cause only nonbloody diarrhea,
some reports indicate that selected SLT-producing,
non-O157:H7 serotypes may have caused cases of
hemorrhagic colitis and HUS in Europe (29,30). In the
United States, disease caused by non-O157:H7 serotype is
rare; however, a recent outbreak of bloody diarrhea in
Montana was suspected to have been caused by a
SLT-II-producing E. coli of serotype O104:H21 (31).

A more relevant finding, and one that has stronger
implications regarding the reliance on sorbitol phenotype
for identifying pathogens, comes from a recent study
which showed that isolates of serotype O157:H7 in
sorbitol-containing foods can mutate from a
sorbitol-nonfermenting to a sorbitol-fermenting phenotype
(32). Moreover, the frequency of isolation of
sorbitol-fermenting O157 strains in Europe appears to be
increasing. In Germany, for instance, strains of serotype
O157:H- that produce SLT-II have been isolated from HUS
patients (33).  Unlike serotype O157:H7, these strains
fermented sorbitol and were positive in the
methyl-umbelliferyl glucuronide assay. Initially, these
strains were considered atypical. However, other studies
confirmed that pathogenic, sorbitol-fermenting, serotype
O157:H- strains were fairly prevalent in HUS patients in
central Europe (34). In another report, serologic and
biochemical characterization of 41 SLT-producing, O157
strains (including H7 and H- serotypes) determined that
as many as 25% of the isolates were sorbitol positive.
Furthermore, there was considerable variation among
pathogenic serotype O157 isolates not only with respect
to sorbitol fermentation, but also with respect to other
phenotypic characteristics (6). These variants are not
detected by sorbitol-containing media and may not be
identified by the routine biochemical tests used to
characterize serotype O157:H7.

The notoriety of recent outbreaks has stimulated the
development of many new assays to detect serotype
O157:H7; some of them may also be useful for detecting
phenotypic variants. Many of these assays use molecular
techniques, and some are commercially available. Several
new molecular subtyping methods have also been
introduced. Although typing methods will not be discussed
here, such techniques as ribotyping, pulsed-field gel
electrophoresis (35), lambda restriction fragment length
polymorphism (36), and others have been extremely useful
in studying the epidemiology of serotype O157:H7 in
foodborne outbreaks.

Phenotypic variants of serotype O157:H7 retain the O157
antigen; hence, antibodies to O157 antigen can be used to
identify both serotype O157:H7 and its variants. In the
clinical laboratory, anti-O157 sera are used effectively
in agglutination or latex agglutination tests to rapidly
screen or serologically confirm isolates. Some anti-O157
antibodies have also been coupled to magnetic beads and
used to selectively isolate this pathogen from foods (37)
or have been incorporated into enzyme immunoassays to
directly detect serotype O157:H7 in foods and clinical
specimens. The latter application of anti-O157 sera,
however, has had some drawbacks.  Many preparations of
anti-O157 sera cross-react with other bacteria, including
Citrobacter freundii (38), E. hermanii, and Yersinia
enterocolitica O:9 (39). Moreover, the O157 antigen is
present on other non-H7 E. coli serotypes (6,40), many of
which are not pathogenic. For example, when anti-O157
serum was used in an analysis of various food products,
nonpathogenic O157 isolates were found that neither
produced SLT nor were of the H7 serotype (27). Therefore,
positive test results of food samples tested with assays
that use anti-O157 sera should be confirmed by other
methods. Pre-absorption of diagnostic antisera to remove
cross-reacting antibodies or the use of antibodies
specific for other non-O157 surface antigens of serotype
O157:H7 may reduce the frequency of serologic
cross-reactions (41).

Phenotypic variants also appear to retain the
pathogenicity of serotype O157:H7 (6,33); therefore,
assays specific for virulence factors are not affected by
the phenotypic variations described above. For example,
anti-SLT antibodies can be used to screen fecal specimens
for toxins, and SLT gene-specific DNA probes and
polymerase chain reaction (PCR) can be used to identify
all SLT-producing pathogens regardless of phenotype.
However, assays specific for SLT or SLT genes do not
provide sufficient data for epidemiologic investigations
and "trace-back" studies. More than 60 E. coli serotypes
have been found to produce SLT (1,2), and even strains
from more distantly related genera, such as C. freundii,
reportedly produce SLT-II-like cytotoxins (42). Many of
these SLT-producing E. coli serotypes have not been
implicated in disease; therefore, the mere detection of
potential SLT-producing strains in foods or in patients'
specimens by these assays is not conclusive evidence that
the bacteria caused the illness.

Some new assays do not have these limitations.  One PCR
assay, designed as a mismatch amplification mutation
assay, preferentially amplifies an allele in the uid A
gene that is unique only to serotype O157:H7, including
its phenotypic variants of serotype O157:H- that are
sorbitol and methyl-umbelliferyl glucuronide positive
(43). Coupled with primers specific for SLT genes, this
multiplex PCR assay can simultaneously identify isolates
of serotype O157:H7 and the type of SLT they encode (44).
Analysis of pure culture isolates showed that this assay
detected all SLT-producing serotypes and was able to
distinguish isolates of serotype O157:H7, including the
phenotypic variants.

Advantages of these new molecular methods include
specificity, sensitivity, and the ability to detect
phenotypic variants of serotype O157:H7. However, these
assays are far too complex and costly for use in the
routine analysis of food or clinical specimens. 
Furthermore, although the emergence of phenotypic
variants is of concern, they have only been observed
sporadically and are not prevalent worldwide. 
Nonetheless, should the frequency of isolation or the
incidence of infection caused by these variants increase
or should other SLT-producing serotypes of E. coli become
more firmly established as causative agents of illness,
other media or assays may need to be incorporated into
existing diagnostic methods. In the interim, the
continued use of a sorbitol-containing medium such as
sorbitol-MacConkey agar to screen bloody stool specimens
is a useful and economical laboratory procedure for the
early diagnosis of serotype O157:H7 infections.

Conclusions

Bovine products have most often been implicated in
foodborne infections with E. coli serotype O157:H7.
However, recent outbreaks indicate that other food types
may also serve as vehicles of transmission for this
pathogen. Most notably, acidic foods that were once
thought to be of low risk can no longer be considered
safe because of the acid-tolerant properties of this
bacterium. Most microbiologic media and diagnostic assays
have been designed specifically to detect serotype
O157:H7. However, there is phenotypic diversity within
the serogroup. Should these variants become more
prevalent in infections, the use of sorbitol medium alone
may become inadequate in detecting the diversity of
strains in this pathogenic serotype.

Acknowledgments

The author thanks G.J. Jackson, FDA, for critical review
of this manuscript and L. Tomlinson, FDA, for editorial
assistance.

Dr. Feng is a research microbiologist with the Food and
Drug Administration in Washington, D.C. He was a
postdoctoral fellow in molecular biology at Purdue
University and a senior scientist at IGEN Inc. His
current research centers on developing rapid diagnostic
methods for detecting foodborne bacterial pathogens. He
is a member of the Microbiology Committee, Association of
Official Analytical Chemists International, and serves as
science advisor to international health organizations and
foreign governments.

Address for correspondence:  Peter Feng (HFS-516), U.S.
Food and Drug Administration, 200 C Street, S.W., 
Washington, DC 20204, USA; fax 202-401-7740; email
pxf@fdacf.ssw.dhhs.gov.

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Bimson J, Sharp JCM. An outbreak of Escherichia coli O157
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16. Morgan D, Newman CP, Hutchinson DN, Walker AM, Rowe
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Environ Microbiol 1991;57:2693-8.
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H. Shiga-like toxin II-related cytotoxins in Citrobacter
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44. Cebula TA, Payne WL, Feng P. Simultaneous
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serotype and their Shiga-like toxin type by
MAMA/multiplex PCR. J Clin Microbiol 1995;33:248-50.





































DISPATCHES

Epidemic-Associated Neisseria meningitidis Detected by
Multilocus Enzyme Electrophoresis

In Oregon and parts of Washington State, the incidence of
serogroup B meningococcal disease increased substantially
in 1994 (1). Multilocus enzyme electrophoresis (MEE)
subtyping of N. meningitidis serogroup B strains
collected in these areas during 1993 and 1994 suggested
that these increases were due to a group of genetically
related strains of the enzyme type-5 (ET-5) complex. ET-5
N. meningitidis serogroup B were first recognized in
Norway in 1974 as the cause of a meningococcal disease
epidemic that persisted through 1991. Since 1974,
serogroup B meningococci of the ET-5 complex have caused
epidemics in Europe, Cuba, and South America; these
epidemics elevated disease rates for many years in the
affected areas (2,3) and led to sustained efforts for
vaccine development. This report describes the use of MEE
to compare invasive N. meningitidis serogroup B
meningococcal strains from Oregon and Washington with
epidemic serogroup B strains from other countries and
with serogroup B strains that have caused endemic disease
in other parts of the United States.

MEE, first described in 1966 as a molecular approach to
the study of genetic variation in eukaryotic systems, has
only gradually been adopted by microbiologists and
epidemiologists. The fundamental concept underlying MEE
is that differences in the electrophoretic mobility of
constitutive enzymes (resulting from amino acid
substitutions) reflect the chromosomal genotype of
strains and thereby allow the calculation of a
genetic-relatedness index (Figure 1 cannot viewd in 
ASCII). As recently as 1984, only one bacterial species, 
Escherichia coli, had been studied by MEE. Since then, 
however, MEE has been used to characterize genetic 
variation among populations of Legionella spp., 
Bordetella spp., Haemophilus influenzae, Streptococcus 
spp., Listeria monocytogenes, Neisseria meningitidis, 
and other bacteria (4).

To carry out MEE, crude aqueous extracts of bacteria are
electrophoresed in a block of 11% to 12% starch in the
presence of a dilute buffer (pH 8.0). The block is then
cut into thin slices, which are stained to detect
specific enzymes. The distance traveled by each enzyme is
used to create a series of numbers representing the set
of enzyme mobilities characteristic of individual
strains. The number of enzymes used is somewhat arbitrary
and varies between organisms; 15 to 24 enzymes have
usually been adequate to characterize genetic diversity
among bacterial populations. For this investigation,
electrophoretic variations in 24 enzymes were used to
describe genetic variability among isolates of N.
meningitidis serogroup B. N. meningitidis strains used
for this analysis were collected from Oregon (1993-1994,
n=64) and part of Washington State (1993-1994, n=17;
1992, n=2; 1990, n=1; unknown, n=2); serogroup B
meningococcal epidemics outside the United States
(1976-1993; Norway n=1; Cuba n=1; Brazil n=1; and Chile
n=2); and active population-based surveillance for
meningococcal disease in selected areas of the United
States (1991-1994, from the San Francisco Bay area,
Georgia, Maryland, Oklahoma, and Tennessee, n=57). The
epidemic strains tested from Norway and Cuba are the type
used for the outer membrane protein vaccines developed
and tested in these countries.

The MEE data analyzed here (Figure 1 cannot be viewed 
in ASCII) suggest that the increased rates of disease
in Oregon and part of Washington are caused by highly
genetically related N. meningitidis serogroup B strains 
of the ET-5 complex. These strains have been relatively 
rare in the United States. Oregon and Washington strains 
match a strain isolated in Santiago, Chile, during 1993. 
The prolonged duration of some ET-5 serogroup B 
meningococcal epidemics in large regions (e.g., Brazil, 
Argentina, and Chile) demands careful monitoring of this 
organism in the United States. Efforts to identify 
potentially modifiable risk factors for the disease and 
develop a vaccine have been intensified. MEE will 
continue to be the primary means for epidemiologic 
tracking and surveillance of ET-5 complex N. 
meningitidis serogroup B in the United States.

Michael W. Reeves,* Bradley A. Perkins*
Marion Diermayer+, and Jay D. Wenger*
*National Center for Infectious Diseases, Centers for
Disease Control and Prevention (CDC),
Atlanta, Georgia, USA
+Emerging Infections Program, Oregon Dept. of Health,
Portland, Oregon, USA, and Epidemiology Program Office,
CDC, Atlanta, Georgia, USA

References

1. Centers for Disease Control and Prevention. Serogroup
B meningococcal disease--Oregon, 1994. MMWR 1995;44:121-4.
2. Caugant DA, Froholm LO, Bovre K, Holten E, Frasch CE,
Mocca LF, Zollinger WD, Selander RK. Intercontinental
spread of a genetically distinctive complex of clones of
Neisseria meningitidis causing epidemic disease. Proc
Natl Acad Sci USA 1986;83:4927-31.
3. Sacchi CT, Pessoa LL, Ramos SR, Milagres LG, Camargo
MCC, Hidalgo NTR, Melles CEA, Caugant DA, Frasch CE.
Ongoing group B Neisseria meningitidis epidemic in S o
Paulo, Brazil, due to increased prevalence of a single
clone of the ET-5 complex. J Clin Microbiol
1992;30:1734-8.
4. Selander RK, Caugant DA, Ochman H, Musser JM, Gilmour
MN, Whittam TS. Methods of multilocus enzyme
electrophoresis for bacterial population genetics and
systematics. Appl Environ Microbiol 1986;51:873-84.















Dengue/Dengue Hemorrhagic Fever:  The Emergence of a
Global Health Problem

Dengue and dengue hemorrhagic fever (DHF) are caused by
one of four closely related, but antigenically distinct,
virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4), of the
genus Flavivirus (1). Infection with one of these
serotypes does not provide cross-protective immunity, so
persons living in a dengue-endemic area can have four
dengue infections during their lifetimes. Dengue is
primarily an urban disease of the tropics, and the
viruses that cause it are maintained in a cycle that
involves humans and Aedes aegypti, a domestic, day-biting
mosquito that prefers to feed on humans. Infection with
a dengue virus serotype can produce a spectrum of
clinical illness, ranging from a nonspecific viral
syndrome to severe and fatal hemorrhagic disease.
Important risk factors for DHF include the strain and
serotype of the virus involved, as well as the age,
immune status, and genetic predisposition of the patient.

The first reported epidemics of dengue fever occurred in
1779-1780 in Asia, Africa, and North America; the near
simultaneous occurrence of outbreaks on three continents
indicates that these viruses and their mosquito vector
have had a worldwide distribution in the tropics for more
than 200 years. During most of this time, dengue fever
was considered a benign, nonfatal disease of visitors to
the tropics. Generally, there were long intervals (10-40
years) between major epidemics, mainly because the
viruses and their mosquito vector could only be
transported between population centers by sailing
vessels.

A global pandemic of dengue begun in Southeast Asia after
World War II and has intensified during the last 15
years. Epidemics caused by multiple serotypes
(hyperendemicity) are more frequent, the geographic
distribution of dengue viruses has expanded, and DHF has
emerged in the Pacific region and the Americas (1,2). In
Southeast Asia, epidemic DHF first appeared in the 1950s,
but by 1975 it had become a leading cause of
hospitalization and death among children in many
countries. In the 1980s, DHF began a second expansion
into Asia when Sri Lanka, India, and the Maldive Islands
had their first major DHF epidemics; Pakistan first
reported an epidemic of dengue fever in 1994. The recent
epidemics in Sri Lanka and India were associated with
multiple dengue virus serotypes, but DEN-3 was
predominant and was genetically distinct from DEN-3
viruses previously isolated from infected persons in
those countries (3).

After an absence of 35 years, epidemic dengue fever
occurred in both Taiwan and the People's Republic of
China in the 1980s. The People's Republic of China had a
series of epidemics caused by all four serotypes, and its
first major epidemic of DHF, caused by DEN-2, was
reported on Hainan Island in 1985 (4). Singapore also had
a resurgence of dengue/DHF from 1990 to 1994 after a
successful control program had prevented significant
transmission for over 20 years (5). In other countries of
Asia where DHF is endemic, the epidemics have become
progressively larger in the last 15 years.

In the Pacific, dengue viruses were reintroduced in the
early 1970s after an absence of more than 25 years.
Epidemic activity caused by all four serotypes has
intensified in recent years with major epidemics of DHF
on several islands (6).

Despite poor surveillance for dengue in Africa, we know
that epidemic dengue fever caused by all four serotypes
has increased dramatically since 1980. Most activity has
occurred in East Africa, and major epidemics were
reported for the first time in the Seychelles (1977),
Kenya (1982, DEN-2), Mozambique (1985, DEN-3), Djibouti
(1991-92, DEN-2), Somalia (1982, 1993, DEN-2), and Saudi
Arabia (1994, DEN-2) (1,6, CDC, unpublished data).
Epidemic DHF has been reported in neither Africa nor the
Middle East, but sporadic cases clinically compatible
with DHF have been reported from Mozambique, Djibouti,
and Saudi Arabia (CDC, unpublished data).

The emergence of dengue/DHF as a major public health
problem has been most dramatic in the American region. In
an effort to prevent urban yellow fever, which is also
transmitted by Ae. aegypti, the Pan American Health
Organization organized a campaign that eradicated Ae.
aegypti from most Central and South American countries in
the 1950s and 1960s. As a result, epidemic dengue
occurred only sporadically in some Caribbean islands
during this period. The Ae. aegypti eradication program,
which was officially discontinued in the United States in
1970, gradually eroded elsewhere, and this species began
to reinfest countries from which it had been eradicated.
In 1995, the geographic distribution of Ae. aegypti was
similar to its distribution before the eradication
program (Figure 1. [cannot be viewed in ASCII].) 

In 1970, only DEN-2 virus was present in the Americas,
although DEN-3 may have had a focal distribution in
Colombia and Puerto Rico (7). In 1977, DEN-1 was
introduced and caused major epidemics throughout the
region over a 16-year period (7). DEN-4 was introduced in
1981 and caused similar widespread epidemics (7). Also in
1981, a new strain of DEN-2 from Southeast Asia caused
the first major DHF epidemic in the Americas (Cuba) (7).
This strain has spread rapidly throughout the region and
has caused outbreaks of DHF in Venezuela, Colombia,
Brazil, French Guiana, Suriname, and Puerto Rico. By
1995, 14 countries in the American region had reported
confirmed DHF cases (Figure 2. [cannot be viewed in ASCII]), 
and DHF is endemic in many of these countries.

DEN-3 virus recently reappeared in the Americas after an
absence of 16 years. This serotype was first detected in
association with a 1994 dengue/DHF epidemic in Nicaragua
(8). Almost simultaneously, DEN-3 was confirmed in Panama
and, in early 1995, in Costa Rica (8, CDC, unpublished
data). In Nicaragua, considerable numbers of DHF were
associated with the epidemic, which was apparently caused
by DEN-3. In Panama and Costa Rica, the cases were
classic dengue fever.

Viral envelope gene sequence data from the DEN-3 strains
isolated from Panama and Nicaragua have shown that this
new American DEN-3 virus strain was likely a recent
introduction from Asia since it is genetically distinct
from the DEN-3 strain found previously in the Americas,
but is identical to the DEN-3 virus serotype that caused
major DHF epidemics in Sri Lanka and India in the 1980s
(R. Lanciotti; unpublished data). The new DEN-3 strain,
and the susceptibility of the population in the American
tropics to it, suggests that DEN-3 will spread rapidly
throughout the region and likely will cause major
epidemics of dengue/DHF in the near future.

In 1995, dengue is the most important mosquito-borne
viral disease affecting humans; its global distribution
is comparable to that of malaria, and an estimated 2.5
billion people are living in areas at risk for epidemic
transmission (Figure 3. [cannot be viewed in ASCII].) Each 
year, tens of millions of cases of dengue fever occur 
and, depending on the year, up to hundreds of thousands 
of cases of DHF. The case-fatality rate of DHF in most 
countries is about 5%: most fatal cases are among children.

There is a small, but significant, risk for dengue
outbreaks in the continental United States. Two competent
mosquito vectors, Ae. aegypti and Aedes albopictus, are
present and, under certain circumstances, each could
transmit dengue viruses. This type of transmission has
been detected twice in the last 15 years in south Texas
(1980 and 1986) and has been associated with dengue
epidemics in northern Mexico (7). Moreover, numerous
viruses are introduced annually by travelers returning
from tropical areas where dengue viruses are endemic.
From 1977 to 1994, a total of 2,248 suspected cases of
imported dengue were reported in the United States (9,
CDC, unpublished data). Although some specimens collected
were not adequate for laboratory diagnosis, preliminary
data indicate that 481 (21%) cases were confirmed as
dengue (9, CDC, unpublished data). Many more cases
probably go unreported each year because surveillance in
the United States is passive and relies on physicians to
recognize the disease, inquire about the patient's travel
history, obtain proper diagnostic samples, and report the
case. These data underscore the fact that southern Texas
and the southeastern United States, where Ae. aegypti is
found, are at risk for dengue transmission and sporadic
outbreaks.

The reasons for this dramatic global emergence of
dengue/DHF as a major public health problem are complex
and not well understood (10). However, several important
factors can be identified. First, effective mosquito
control is virtually nonexistent in most dengue-endemic
countries. Considerable emphasis for the past 20 years
has been placed on ultra-low-volume insecticide space
sprays for adult mosquito control, a relatively
ineffective approach for controlling Ae. aegypti. Second,
major global demographic changes have occurred, the most
important of which have been uncontrolled urbanization
and concurrent population growth. These demographic
changes have resulted in substandard housing and
inadequate water, sewer, and waste management systems,
all of which increase Ae. aegypti population densities
and facilitate transmission of Ae. aegypti-borne disease.
Third, increased travel by airplane provides the ideal
mechanism for transporting dengue viruses between
population centers of the tropics, resulting in a
constant exchange of dengue viruses and other pathogens.
Lastly, in most countries the public health
infrastructure has deteriorated. Limited financial and
human resources and competing priorities have resulted in
a "crisis mentality" with emphasis on implementing
so-called emergency control methods in response to
epidemics rather than on developing programs to prevent
epidemic transmission. This approach has been
particularly detrimental to dengue control because, in
most countries, surveillance is very inadequate; the
system to detect increased transmission normally relies
on reports by local physicians who often do not consider
dengue in their diagnoses. As a result, an epidemic has
often reached or passed the peak of transmission before
it is detected.

No dengue vaccine is available. Recently, however,
attenuated candidate vaccine viruses have been developed
in Thailand. These vaccines are safe and immunogenic when
given in various formulations, including a quadrivalent
vaccine for all four dengue virus serotypes.
Unfortunately, efficacy trials in human volunteers have
yet to be initiated. Research is also being conducted to
develop second-generation recombinant vaccine viruses;
the Thailand attenuated viruses are used as a template.
However, an effective dengue vaccine for public use will
not be available for 5 to 10 years. 

Prospects for reversing the recent trend of increased
epidemic activity and geographic expansion of dengue are
not promising. New dengue virus strains and serotypes
will likely continue to be introduced into many areas
where the population densities of Ae. aegypti are at high
levels. With no new mosquito control technology
available, in recent years public health authorities have
emphasized disease prevention and mosquito control
through community efforts to reduce larval breeding
sources (11). Although this approach will probably be
effective in the long run, it is unlikely to impact
disease transmission in the near future. We must,
therefore, develop improved, proactive, laboratory-based
surveillance systems that can provide early warning of an
impending dengue epidemic. At the very least,
surveillance results can alert the public to take action
and physicians to diagnose and properly treat dengue/DHF
cases.

Duane J. Gubler and Gary G. Clark
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Fort Collins, Colorado, and San Juan, Puerto Rico, USA

References

1. Gubler DJ. Dengue. In: Epidemiology of arthropod-borne
viral disease, Monath TPM, editor. Boca Raton (FL): CRC
Press, 1988:223-60.
2. Halstead SB. The XXth century dengue pandemic: need
for surveillance and research. Rapp Trimest Statist Sanit
Mondo 1992;45:292-8.
3. Lanciotti RS, Lewis JG, Gubler DJ, Trent DW. Molecular
evolution and epidemiology of dengue-3 viruses. J Gen
Virol 1994;75:65-75.
4. Qiu FX, Gubler DJ, Liu JC, Chen, QQ. Dengue in China:
a clinical review. Bull WHO 1993;71:349-59.
5. Anonymous. The dengue situation in Singapore.
Epidemiol Bull 1994;20:31-3.
6. Gubler DJ. Dengue haemorrhagic fever: a global update
[Editorial]. Virus Information Exchange News. 1991;8:2-3.
7. Gubler DJ. Dengue and dengue haemorrhagic fever in the
Americas. In: WHO, Regional Office for SE Asia, New
Delhi, Monograph. SEARO 1993;22:9-22.
8. Centers for Disease Control and Prevention. Dengue
type 3 infection--Nicaragua and Panama, October-November
1994. MMWR 1995;44:21-4.
9. Rigau-P rez JG, Gubler DJ, Vorndam AV, Clark GG.
Dengue surveillance--United States, 1986-1992. MMWR
1994;43:7-19.
10. Gubler DJ, Trent DW. Emergence of epidemic
dengue/dengue hemorrhagic fever as a public health
problem in the Americas. Infect Agents Dis 1994;2:383-93.
11. Gubler DJ, Clark GG. Community-based integrated
control of Aedes aegypti: a brief overview of current
programs. Am J Trop Med Hyg 1994:50:50-60.



























Progress Toward the Eradication of Dracunculiasis (Guinea
Worm Disease): 1994

Dracunculiasis, or guinea worm disease (GWD), is a
disabling infection caused by the nematode parasite
Dracunculus medinensis. The disease is endemic in India,
Africa, and the Middle East. People become infected when
they drink water containing tiny crustaceans, called
copepods or "water fleas," that act as intermediate hosts
of the organism and harbor infective larvae. When the
ingested copepods are killed by the digestive juices in
the stomach, the larvae are released and move to the
small intestine. They penetrate the intestinal wall and
migrate to the connective tissues of the thorax, where
male and female larvae mature and mate 60 to 90 days
after infection. Over the next year, female worms grow to
maturity, reach a length of 70 cm or more (2-3 feet), and
slowly migrate to the surface of the body. Worms emerge
from the lower extremities in about 90% of cases, but
they can also appear in the upper extremities, the trunk,
buttocks, genitalia, or other parts of the body.

Infected persons remain asymptomatic for approximately a
year after infection when the mature female worm
approaches the skin and forms a painful papule in the
dermis. This papule can become a blister within 24 hours
or may enlarge for several days before becoming a
blister. Eventually it ruptures, exposing the worm.
Shortly before the skin lesion forms, pronounced systemic
symptoms may occur, including erythema and urticarial
rash with intense pruritus, nausea, vomiting, diarrhea,
and dizziness. On contact with fresh water, a loop of the
worm's uterus opens and discharges a swarm of motile
larvae. This process may be repeated, if the lesion is
resubmerged in water, until the entire brood of larvae is
discharged. Larvae ingested by copepods mature in the
body cavity of the intermediate host in about 2 weeks.
Stagnant sources of drinking water such as ponds,
cisterns, pools in dried-up river beds, temporary
hand-dug wells, and step-wells commonly harbor
populations of freshwater copepods and are the usual
sites where the infection is transmitted.

As the worm emerges through the skin lesion, the affected
person pulls it out slowly and carefully, usually by
winding a few centimeters each day on a stick. This very
painful process may last many weeks. Pain and other
symptoms may lessen with the rupture of the blister, but
at this time pyogenic organisms often invade the
superficial lesion and worm tract and aggravate the
condition. If the worm breaks during traction, an intense
inflammatory reaction occurs, with pain, swelling, and
cellulitis along the worm track. Infected persons are
often incapacitated for several weeks, or for months, if
complications caused by secondary bacterial infections
ensue.

Infected persons do not develop immunity, and there is no
cure for GWD. Pain from emerging worms may be relieved by
applying wet compresses to the lesion or by immersing the
lesion in a container of water, and then safely disposing
of the released larvae. Placing an occlusive bandage on
the wound to keep it clean prevents the patient from
contaminating sources of drinking water. Once the worm
appears, oral medications to relieve the associated pain
and topical antiseptics or antibiotic ointment to
minimize the risk for secondary infections allows the
worm to be removed by gentle traction over a number of
days.

The World Health Organization (WHO) has targeted GWD for
eradication by the end of 1995. A coalition of agencies,
institutions, and organizations are providing technical
and financial assistance to national eradication
programs.

An understanding of the factors that contribute to the
emergence of dracunculiasis provides the basis for the
current elimination program. GWD can be eradicated for
several reasons: 1) there is no human carrier beyond the
1-year incubation period; 2) there is no known animal
reservoir; 3) detection of patent infections (i.e., worms
protruding from skin lesions) is an easy way to assess
the presence of the disease in communities, and
protrusion of the worm is required for transmission;
4) transmission of the disease is markedly seasonal,
facilitating the timing and effectiveness of surveillance
and control interventions, including containment of
cases; 5) the methods for controlling transmission are
simple, and 6) the disease is well recognized by the
local population in areas where it is endemic.

The overall strategy of national GWD eradication programs
includes three operational phases: l) conducting baseline
surveys to identify villages where the disease is
endemic; 2) training village-based health workers to use
case registries for monthly surveillance and to implement
control interventions in affected communities; and 3)
using case-containment, i.e., prompt detection of all
remaining cases (before or within 24 hours of worm
emergence), treatment of the lesions to prevent
transmission, and close supervision of village-based
health workers to ensure that each case has been properly
contained (1).

The thrust of control interventions is to educate
affected persons about the origin of the disease and
about the measures they and their communities can take to
prevent it. Affected households are provided with cloth
filters and taught how to safely use them to remove the
copepods from water. Household members are also taught
that those with emerging worms should be kept from
entering sources of drinking water. Other control
interventions include providing safe drinking water to
affected villages and selectively using the insecticide
temefos to reduce copepod populations.

In 1986, an estimated 3.32 million cases of GWD occurred
in Africa (2). That same year, only 22,610 cases of GWD
were reported from India, the only affected country with
a national eradication campaign then underway. Worldwide
cases reported to WHO have declined from 781,219 in 1988
to 221,055 in 1993 (3). By 1990, 9 of the 19 affected
countries had initiated eradication programs and had
conducted baseline surveys to assess the extent of GWD
(Figure 1. [cannot be viewed in ASCII], Table 1). At the 
end of 1994, all 19 countries were actively combating 
the diseases, and the provisional number of cases 
reported to WHO was 164,750 (Figure 2. [cannot be viewed 
in ASCII], Table 2). The number of affected villages 
was reduced from more than 23,000 in 1993 to fewer 
than 10,000; 52% of the affected villages were in 
the case-containment phase.

Table 1.  Dracunculiasis cases reported, 1990*
_________________________________________________________
Country                                 Number of cases
_________________________________________________________
Nigeria                                     394,082
Ghana                                       117,034
Burkina Faso                                 42,187
Benin                                        37,414
Mauritania                                    8,036
India                                         4,798  
Togo                                          3,042  
Cameroon                                        742
Pakistan                                        160
Chad+                                             -
Cote d'Ivoire+                                    -
Ethiopa+                                          -
Kenya+                                            -
Mali+                                             -
Niger+                                            -
Senegal+                                          -
Sudan+                                            -
Uganda+                                           -
Yemen+                                            -
_________________________________________________________
*Cases reported to the World Health organization from 
countries completing national case searches or from active
village-based surveillance.
+No information available at this time.


Table 2.  Dracunculiasis cases reported, 1994*
_________________________________________________________
Country                                 Number of cases
_________________________________________________________
Sudan                                        53,092
Nigeria                                      39,774
Niger                                        23,568
Uganda                                       10,409
Ghana                                         8,432   
Burkina Faso                                  6,859  
Mali                                          5,396  
Togo                                          5,045  
Mauritania                                    5,029  
Cote d'Ivoire                                 4,700  
Benin                                         3,440  
Ethiopia                                      1,252  
Chad                                            640
India                                           371
Senegal                                         186
Yemen                                            74
Kenya                                            37
Cameroon                                         30
Pakistan                                          0
_________________________________________________________
*Provisional data reported to the World Health 
Organization from countries completing national case 
searches or from active village-based surveillance. 
Sudan's report to WHO includes cases reported by the
Passive Surveillance System.


In 1994, Pakistan had no cases (4). (Pakistan is the
first country where GWD was endemic during the 1980s to
have eliminated indigenous transmission of the disease
for 1 year.) Yemen reported small foci of disease
transmission for the first time in several years, and
Sudan reported 28,899 GWD cases during active
village-based searches, and through its passive
surveillance system (5). In early March 1995, Sudan
revised the number of cases reported to WHO for 1994 to
53,092 cases. Although the number of cases reported by
Sudan may not be precise, their relative magnitude likely
reflects that the incidence of disease there exceeds that
reported by any of the other affected countries.

The global GWD eradication campaign faces two major
challenges in 1995: to complete implementation of the
case-containment strategy and other control
interventions, such as insecticide use, in villages of
all affected countries and to mobilize greater public
support in these countries. The countries that pose the
greatest eradication challenge are Sudan, Niger, and
Nigeria. However, even in the countries with the fewest
cases, markedly tighter control measures will be required
to completely interrupt transmission of GWD by the end of
1995. Success of the eradication campaign depends on
continued funding and on the ability of national programs
and collaborating agencies and organizations to complete
the needed surveillance and control interventions.

Ernesto Ruiz-Tiben, Donald R. Hopkins, Trenton K.
Ruebush,* and Robert L. Kaiser
Global 2000 Project, The Carter Center of Emory
University, Atlanta, Georgia, USA
*National Center for Infectious Diseases, Centers for
Disease Control and Prevention, Atlanta, Georgia, USA
 
References

1. Hopkins DR, Ruiz-Tiben E. Strategies for
dracunculiasis eradication. Bull WHO 1991;69:533-40.
2. Watts S. Dracunculiasis in Africa in 1986: its
geographic extent, incidence, and at-risk population. Am
J Trop Med Hyg 37:119-25.
3. WHO. Dracunculiasis--global surveillance summary 1993.
Wkly Epidemiol Rec 1995:17:121-8.
4. Centers for Disease Control and Prevention. Update:
dracunculiasis eradication--Pakistan, 1994. MMWR
1995;44:117-9.
5. WHO. Dracunculiasis update--Sudan. Wkly Epidemiol Rec
1995:7:48-50.













LETTERS

Heat-Stable Enterotoxin-Producing Escherichia coli
O169:H41 in Japan

To the Editor: Enterotoxigenic Escherichia coli (ETEC)
cause diarrhea by producing either a heat-labile
enterotoxin, a heat-stable enterotoxin (ST), or both.
Consequently, ETEC can be identified either by detecting
the enterotoxin in the culture fluid by immunologic
assays or by detecting enterotoxin-coding genes with DNA
probes or polymerase chain reaction (PCR) amplification.
For many clinical laboratories, however, serologic typing
is the most common test used to determine if isolates are
members of known pathogenic groups.

Although E. coli serotype O169:H8 has been recognized as
one of the ETEC strains (1), serotype O169:H41 is not
established worldwide as one of the diarrheagenic E. coli
of the ETEC group. Ando et al. first reported that an
outbreak at a school for physiologically handicapped
children in Saitama Prefecture was due to ST-producing E.
coli serotype O169:H41 (2). We report an outbreak of
diarrhea caused by E. coli O169:H41 that predates the
outbreak reported by Ando et al. and information about
additional outbreaks in Japan since 1991.

In June 1991, we isolated toxigenic E. coli from the
stool of two of three ill members of an eight-member
family during an outbreak of diarrheal illness in Osaka,
Japan. An epidemiologic investigation implicated pickles
(kimchi) purchased during a visit to Korea; only the
three members of the family who ate the pickles became
ill. The major symptoms were diarrhea (3/3), abdominal
pain (2/3), and fever (2/3) of  38  C. The incubation
period was estimated at 33 hours. The serotype of these
ST-producing E. coli isolates was not recognized
immediately because the cultures were non-typable by the
lot of E. coli antiserum available when the cultures were
first isolated. The cultures were identified as E. coli
O169:H41 when a new lot of antiserum became available.

In another outbreak investigated by the Osaka City
Department of Environment and Health and the Osaka
Prefecture Department of Environment and Health, food
poisoning occurred among 776 of 1,242 guests of wedding
receptions held at a wedding facility during September
1993. The main symptoms were diarrhea (98%) and abdominal
cramps (74%), and the mean incubation period was 40.5
hours. E. coli O169:H41 was isolated from the stool
specimens of 7 of 14 patients. A strain of E. coli
O169:H41 was isolated from frozen, ready-to-eat seafood
recovered from a distributor who provided foods to the
wedding facility.

In addition to the outbreaks mentioned above, Japanese
surveillance reports describe foodborne outbreaks in
different prefectures between January 1991 and September
1994. In addition to being cultured for E. coli, stools
were also routinely cultured for Shigella, Salmonella
(including typhi and paratyphi), Vibrio, Clostridium,
Aeromonas, Plesiomonas, Bacillus cereus, and
Staphylococcus aureus. Stools were also examined for
rotaviruses and small round viruses by electron
microscopy. E. coli serotype O169:H41 was isolated from
patients' stools in 11 of 40 outbreaks; recovery rates
were 10%-100%. In 7 of the 11 outbreaks, recovery rates
of serotype O169:H41 exceeded 75%. PCR was used to
examine the diarrheagenicity of 31 E. coli isolates
selected from reported outbreaks that occurred from 1991
to 1994 (3). ST production of the 31 isolates was also
examined by COLI ST EIA (Denka Seiken Co., Ltd., Tokyo,
Japan), a competitive enzyme-linked immunosorbent assay
(ELISA) for toxigenic and invasive strains of E. coli.
Strains were grown in Casamino Acids-Yeast Extract broth
shaken at 37  C for 18 hours. The supernatant obtained
after the centrifugation of cells was used for the test
according to the manufacturer's instructions.

Thirty of the 31 E. coli O169:H41 isolates tested
demonstrated toxigenicity by both PCR and ELISA.
Collaborative studies are in progress to further
characterize these isolates and to study the
relationships between different isolates by molecular
epidemiologic methods. Five cultures of E. coli O169:H41
have been ribotyped by a digoxigenin-labeled (Genius
System, Boehringer Mannheim) probe prepared from pKK3535
according to the manufacturer's instructions. The
resulting patterns were indistinguishable when the
restriction enzymes EcoRI, SmaI, BglII, BamHI, SalI,
PstI, or HindIII were used to digest chromosomal DNA.

We suggest that this comparatively new serotype of ETEC
may be spreading across Japan and urge that studies be
conducted to determine its distribution and association
with gastroenteritis worldwide.

References

1. Orskov I, Orskov F, Rowe B. Six new Escherichia coli
O groups O165, O166, O167, O168, O169, and O170. Acta
Pathol Microbiol Immunol Scand Sect B 1984;92:189-93.
2. Ando K, Itaya T, Aoki A, Saito A, Masaki H, Tokumaru
Y. An outbreak of food poisoning caused by
enterotoxigenic Escherichia coli O169:H41. Jpn J Food
Microbiol 1993;10:77-81.
3. Itoh F, Ogino T, Itoh K, Watanabe H. Differentiation
and detection of pathogenic determinants among
diarrheagenic Escherichia coli by polymerase chain
reaction using mixed primers. Jpn J Clin Med
1992;50:343-7.

Yoshikazu Nishikawa, Masaki Hanaoka, Jun Ogasawara,
Nelson P. Moyer,* and Teruo Kimura
Osaka City Institute of Public Health and Environmental
Sciences, Osaka 543, Japan
*Hygienic Laboratory, University of Iowa, Iowa City, Iowa
52242-5002, USA











The GAP Project in Southeastern Turkey: The Potential for
Emergence of Diseases

To the Editor: The undersigned, representing interested
scientists from both Turkey and the United States,
recently visited the water development projects in
southeastern Anatolia, Turkey. This letter describes our
observations and projections on the possible
health-related consequences of these projects with
specific emphasis on infectious diseases.

When new irrigation schemes are introduced into
previously dry areas, disease frequently follows the new
water. The Southeastern Anatolia Irrigation Project or
GAP (its Turkish acronym) is one of the largest projects
ever undertaken in Turkey. This water resources
development program includes the construction of 22 dams
and 19 hydroelectric plants on the Euphrates and Tigris
rivers in southeastern Turkey. Upon completion, the
project will also include an irrigation network for 1.7
million hectares of land, covering eight provinces
corresponding to approximately 10% of Turkey's total
population and surface area (1). In its entirety, GAP
comprises investments in development projects linked to
agriculture, energy, transportation, telecommunications,
health care, education, and urban and rural
infrastructures. To ensure the success of the project, an
agency has been established (the Republic of Turkey Prime
Ministry Southeastern Anatolia Project Regional
Development Administration) to oversee and implement all
of these projects.

The largest of the completed dams on the Euphrates River
is the Ataturk Dam. It is the sixth-largest rock-filled
dam in the world; its hydroelectric systems have already
produced more than seven billion kilowatt hours of power
since 1992 (2). Water from the Ataturk Dam reservoir is
diverted to the plains of upper Mesopotamia through the
Sanliurfa Irrigation Tunnel System. This system consists
of two parallel tunnels, each 26.5-km long and 7.62 m in
diameter, and numerous other irrigation networks and
canal systems. The first water started to flow to the
plains of Harran in November 1994. Additional lands will
be incorporated into the irrigation scheme as the canals
are completed. (The year 2020 is the target date for
completion.) When fully operational, GAP is expected to
double Turkey's hydroelectric production, increase
irrigated areas by 50%, more than double the per capita
income in the region, more than quadruple the gross
national product, and create two million new jobs in the
coming decade (3). The total surface area affected by the
irrigation scheme is about 75,000 km2; of this, 46.2% is
cultivated (36% semiarid rain-fed farmland), 33.3% is dry
pastures, 20.5% is forest and bush.

One of GAP's major goals is to remove the socioeconomic
disparity between the country's more developed regions
and the project area. For GAP to reach its targeted and
sustainable economic aims, projects in various other
sectors also need to be considered and integrated. In
this context, the public health consequences of emerging
diseases in this setting must be anticipated so that
appropriate health education and disease prevention
measures can be implemented.

To anticipate changing patterns in disease associated
with microclimatic and other environmental changes,
knowledge of existing diseases in the region is vital.
Since arthropods, reservoir animals, and other
intermediate hosts are involved in the transmission of
many waterborne parasitic diseases, a clear understanding
of the existing species--especially of insect vectors--is
equally important.

Historically, occasional cases of malaria have occurred
in the region; however, limited records show that this
disease is clearly on the rise. Cutaneous leishmaniasis
is also endemic and on the rise, but few data are
available on the prevalence of the visceral form of the
disease. Other common diseases in the region include
bacterial and helminthic gastrointestinal infections as
well as trachoma.

According to data from the Malaria Division of the
Turkish Health Ministry, the reported cases of Plasmodium
vivax malaria rose from 8,680 in 1990 to 18,676 in 1992
(4). The province of Sanliurfa (population one million in
1990), which is at the heart of the irrigated plains in
GAP, has reported that malaria cases increased from 785
in 1990 to 5,125 in 1993. The numbers of cases in the
first 9 months of 1994 alone were already significantly
higher than those reported in 1993 (S. Aksoy, unpublished
data). Although presumably P. vivax malaria is most
common, cases of P. falciparum malaria have also been
reported in the country. Three cases of P. falciparum
malaria were recently documented in Izmir, which is on
the Aegean Sea coast of Turkey (4). No cases of
drug-resistant malaria have been reported.

Another endemic disease on the rise in the southeastern
region is leishmaniasis, transmitted by biting sand
flies. In Sanliurfa the number of documented cases of the
cutaneous form of this disease has risen from 552 in 1990
to 1,955 in 1993. In the first 9 months of 1994 alone,
the number of reported cases was more than 3,000 (S.
Aksoy, unpublished data). At Sanliurfa's Diyarbakir
Hospital, in 1991, in addition to cases of the cutaneous
forms of the disease, there were 80 potential cases of
visceral leishmaniasis (kala-azar) in children ages 2 to
10 (5). Leishmania donovani is often the causative agent
of kala-azar, but both L. tropica and L. infantum may
also be involved (6). As the economic opportunities in
the GAP provinces attract populations to the region,
visceral leishmaniasis may become a greater threat. The
prevalence of the sand-fly species in the region, their
habitats, and the future implications of the
microclimatic changes for these habitats must be studied
to anticipate future disease patterns.

Other prevalent pathogens in the region include Entamoeba
histolytica, Giardia lamblia, and Ascaris lumbricoides.
Of 22,468 stool samples examined in one study, over 90%
carried intestinal parasites; in children from infancy to
5 years of age, 60% contained Giardia intestinalis (7).
In a second study in Diyarbakir involving 4,670 patients
(ages<1-65 years), the incidence of protozoan and
helminthic infection was approximately 16% (53%, E.
histolytica; 31%, G. lamblia; and 10%, A. lumbricoides)
(8). In both studies, the incidence of amebiasis was
approximately 8% to 9%. In 1989, a survey conducted among
1,001 children in four elementary schools in Sanliurfa
found parasites in 88% of the stool samples examined (50%
Ascaris, 53% Trichuris trichiura, 22% Giardia, 11%
Entamoeba coli) (9). Ancylostomiasis, which occurs in the
eastern Mediterranean, is a potential danger for the
region (10).

The emergence of schistosomiasis, which can quickly reach
epidemic proportions in water-related projects unless
measures are taken, should not be ignored. A recent study
in Sanliurfa has identified Bulinus truncatus, the snail
vector of Schistosoma haematobium in the region (11).
Whether other regions in GAP also harbor this species is
not known, although there have been reports of these
snails in the Nusaybin and Mardin regions (12). A few
decades ago, sporadic cases of disease were also reported
from southeastern regions (13). As microclimatic changes
occur in the GAP area, the presence of these snails and
the potential emergence of schistosomiasis should be
closely monitored.

The costs of combating epidemic diseases can be very
large, whereas the costs of prevention are much lower.
Large national projects that anticipate economic benefits
may sometimes overlook the distant prospects of disease.
Ideally, health planning should be built into a project
from its inception for small funds invested for
prevalence studies early on can bring high returns later.
Earlier dam projects in Senegal, Lake Volta, and Egypt
have shown that unless effective measures are taken
early, infections can quickly reach epidemic levels (14).
The establishment of good surveillance and recording
systems is an important first step.

Serap Aksoy,* Sedat Ariturk+, Martine Y.K. Armstrong,*
K.P. Chang++, Zeynep D rtbudak,* Michael Gottlieb,   M.
Ali Ozcel, **Frank F. Richards,* and Karl Western 
*Yale Univerity School of Medicine,
New Haven, Connecticut
+Dicle University, Diyarbakir, Turkey
++Chicago Medical School, Illinois
 National Institute of Allergy and Infectious Diseases,
**National Institutes of Health, Bethesda, Maryland
Ege University Medical Faculty, Bornova, Izmir, Turkey

References

1. Republic of Turkey Prime Ministry. GAP action plan.
Ankara, Turkey: GAP Regional Development Administration,
1993 (in Turkish).
2. Republic of Turkey Prime Ministry. GAP status report
(1993). Ankara, Turkey: GAP Regional Development
Administration, 1993 (in Turkish).
3. Republic of Turkey Prime Ministry. Agricultural
commodities marketing survey and planning of crop pattern
for GAP. Ankara, Turkey: GAP Regional Development
Administration, 1992.
4. Ok UZ, Buke M, Sayiner AA,  zcel MA. Three Falciparum
malaria cases in Izmir. Acta Parasitologica Turcica
1994;18:33.
5.  zerdem N, Mete  . The interpretation of diagnostic
methods in kala-azar (visceral leishmaniasis) infection.
Acta Parasitologica Turcica 1993;17:1-6.
6. Qy J-Q, Zhong L, Yasinzai-Mascom, M, et al.
Serodiagnosis of Asian leishmaniasis with a recombinant
antigen from the repetitive domain of a Leishmania
kinesin. Trans R Soc Trop Med Hyg 1994;88:543-5.
7. Duran G, Mete  . The epidemiological evaluation of
intestinal parasites in our region. Acta Parasitologica
Turcica 1993;17:35.
8. Balikci E,  zel MF, Mete  . The investigation of
intestinal parasites on the stool flora in patients who
were admitted to microbiology laboratory. Acta
Parasitologica Turcica 1993;17:27.
9. Unat EK, Akaslan I, Akaslan S, et al. Results of the
parasitological examination of stools from students of
our elementary schools in Sanliurfa. Acta Parasitologica
Turcica 1989;13:75.
10. Unat EK, et al. Medical parasitology. Istanbul:
Istanbul University Press;1983:323.
11. Sesem R, Yildirim MZ. Life cycle of Bulinus truncatus
(Audouin 1827) (Pulmonata:Gastropoda) under laboratory
conditions. Acta Parasitologica Turcica 1994;18:337.
12. Paydak F. Systematic analysis of freshwater
gastropods in Diyarbakir, Urfa and Mardin. Diyarbakir
Medical School Proceedings 1967;5:243. 
13. Cebeci M. Intestinal diseases in East Mediterranean
regions. Istanbul University Med Faculty J.
1959;22:701-5.
l4. Stanley NF, Alpers MP. In. Man-made lakes and human
health. London: Academic Press, 1975.






































COMMENTARY

Action Plan for Drug-Resistant Streptococcus pneumoniae

Streptococcus pneumoniae is a leading cause of illness
and death in the United States. It accounts for an
estimated 3,000 cases of meningitis, 50,000 cases of
bacteremia, 500,000 cases of pneumonia, and more than
seven million cases of otitis media annually (1, 2). S.
pneumoniae had been almost uniformly susceptible to
penicillin; however, with the development and worldwide
spread of drug-resistant S. pneumoniae (DRSP), a public
health challenge has emerged. Studies from Australia,
Southeast Asia, Africa, and Europe have reported
pneumococcal strains resistant to penicillin and other
drugs (3). Surveillance data collected at the Centers for
Disease Control and Prevention (CDC) have shown that
high-level resistance to penicillin increased more than
60-fold--from 0.02% for 1979-1987 to 1.3% in 1992--for
pneumococcal isolates from invasive infections (4). In
some communities, at least 30% of isolates are
nonsusceptible to penicillin (5; CDC, unpublished data).

Pneumococcal resistance has been reported for
beta-lactams, macrolides, chloramphenicol, and
sulfonamides. As multidrug-resistant strains become
increasingly prevalent, treatment options will become
limited. The clinical impact of antimicrobial resistance
on the outcome of invasive and noninvasive DRSP
infections remains largely unknown. Vancomycin has been
required to treat patients with pneumococcal meningitis
caused by strains resistant to extended-spectrum
cephalosporins (e.g., cefotaxime and ceftriaxone) (6).
Optimal treatment regimens for DRSP infections remain to
be defined; CDC is organizing a working group to develop
consensus guidelines for the management of pneumococcal
infections.

The prevalence of pneumococcal resistance to
antimicrobial drugs is not known for most areas of the
United States since DRSP infection has not been a
reportable condition. Some studies have suggested great
geographic and temporal variation in levels of
resistance; prevalence rates are 2% to 30% (5,7). In
addition, DRSP can spread rapidly through a population,
and the prevalence of resistant isolates can differ in
adults and children. To make appropriate empiric
antimicrobial choices, clinicians need a reliable and
current assessment of the level of antimicrobial
resistance in the community.

To address the growing problem of DRSP, a working group
of public health practitioners, health care providers,
clinical laboratorians, and representatives of key
professional societies was formed in June 1994. The group
identified the development of an electronic,
laboratory-based surveillance system for DRSP as the
essential first step to address this concern. The group
has issued a comprehensive plan, "A National Strategy for
the Surveillance, Applied Research, Control, and
Prevention of DRSP," to be published in June 1995. This
plan focuses on three public health priorities: 1) to
define and monitor the prevalence and geographic
distribution of DRSP and recognize the emergence of
patterns of resistance, 2) to study further the
epidemiology of DRSP, and 3) to minimize the
complications of DRSP infections through control and
prevention.

The working group has begun piloting an electronic,
laboratory-based surveillance network to detect serious
illness due to DRSP. For isolates nonsusceptible to
oxacillin (zone size <20 mm), minimal inhibitory
concentrations should routinely be determined for
penicillin, an extended-spectrum cephalosporin,
chloramphenicol, vancomycin, and other clinically
relevant drugs. These data will be analyzed to determine
community-specific levels of resistance and will be made
available to clinicians to improve antimicrobial use.
Additionally, aggregate data will be sent to CDC so that
national trends in pneumococcal resistance can be
identified and reported.

Clinical laboratory directors, large commercial
laboratory operators, and laboratory software
manufacturers indicate that many laboratory software
systems can accommodate a paperless, automated mechanism
for reporting communicable disease information directly
to public health authorities. DRSP surveillance may thus
serve as a model for electronic, laboratory-based
reporting for other laboratory-reportable conditions.
Although improved data flow should increase the number
and timeliness of reported cases, a strategy for ensuring
quality control of data will be required. 

In the era of emerging antimicrobial resistance,
prevention of pneumococcal infections is paramount;
vaccination strategies offer an important approach to
controlling DRSP. An existing pneumococcal polysaccharide
vaccine that can prevent a substantial number of
pneumococcal infections, including those caused by DRSP,
is underutilized. The vaccine is recommended by the
Advisory Committee for Immunization Practices (ACIP) for
use in persons older than 2 years of age who have certain
underlying medical conditions and for all persons older
than 65 years of age (8). It is not recommended for
routine use among children under 2 years of age because
it does not provide immunity consistently in this age
group. An effective vaccine is needed to prevent
pneumococcal infections in this population, which has the
highest risk for otitis media and meningitis caused by
DRSP. If the prevalence of pneumococcal infection (and
therefore antimicrobial use) can be substantially reduced
by vaccination, the impact of DRSP may diminish. Novel
vaccine demonstration projects supported by federal and
state health agencies are under way to explore means of
increasing coverage with the effective 23-valent
pneumococcal polysaccharide vaccine.

Applied research is also needed to address the problem of
DRSP. CDC has recently funded population-based
investigations to define risk factors, patterns of
transmission, costs, and health outcomes associated with
DRSP. Public health programs for control and prevention
of DRSP are being designed for use at local, state, and
federal levels. Because unnecessary use of antimicrobial
agents has contributed to the emergence of resistant
bacteria (1, 3, 5), educational materials and campaigns
are being developed for both health care providers and
consumers to raise awareness of the link between
excessive antimicrobial use and the emergence of
drug-resistant organisms. Through a multifaceted
approach, the growing problem of DRSP can be addressed to
minimize the complications and costs of resistant
pneumococcal infections. Surveillance for DRSP is an
important starting point from which control and
prevention solutions can proceed.

For more information regarding DRSP activities at CDC,
write to Division of Bacterial and Mycotic Diseases,
NCID, CDC Mailstop C-09, 1600 Clifton Rd., Atlanta, GA
30333 or send an e-mail to DRSP@ciddbd1.em.cdc.gov.

Martin S. Cetron, Daniel B. Jernigan, Robert F. Breiman,
and the DRSP Working Group*
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, Georgia, USA

*Guthrie Birkhead, New York State Department of Health and
the Council of State and Territorial Epidemiologists
(CSTE); Jay C. Butler, CDC; Mathew L. Cartter,
Connecticut Department of Public Health and Addiction
Services; Joan P. Chesney, American Academy of
Pediatrics; William Craig, Infectious Diseases Society of
America; Robert P. Gaynes, CDC; Mary J. R. Gilchrist,
American Society of Microbiologists; Richard E. Hoffman,
Colorado Department of Public Health and Environment and
CSTE; James Jorgensen, National Committee for Clinical
Laboratory Standards; David Klein, National Institute of
Allergy and Infectious Diseases, National Institutes of
Health; Thomas O'Brien, World Health Organization
Collaborating Center for Antibiotic Resistance, Boston;
Benjamin Schwartz, CDC; Albert Sheldon, Jr., Food and
Drug Administration; Kenneth C. Spitalny, New Jersey
State Department of Health; Fred C. Tenover, CDC; and
Ralph J. Timperi, Association of State and Territorial
Public Health Laboratory Directors.

References

1. Reichler MR, Allphin AA, Breiman RF, et al. The spread
of multiply resistant Streptococcus pneumoniae at a day
care center in Ohio. J Infect Dis 1992;166:1346-53.
2. Stool SE, Field MJ. The impact of otitis media.
Pediatr Infect Dis J 1989;8:S11-S14.
3. Klugman KP. Pneumococcal resistance to antibiotics.
Clin Microbiol Rev 1990;3:171-96.
4. Breiman RF, Butler JC, Tenover FC, Elliott JA, Facklam
RR. Emergence of drug-resistant pneumococcal infections
in the United States. JAMA 1994;271:1831-5.
5. Centers for Disease Control and Prevention.
Drug-resistant Streptococcus pneumoniae--Kentucky and
Tennessee, 1993. MMWR 1994;43:23-5,31.
6. Leggiadro RJ, Barrett, FF, Chesney PJ, Davis Y,
Tenover FC. Invasive pneumococci with high level
penicillin and cephalosporin resistance at a mid-South
children's hospital. Pediatr Infect Dis J 1994;13:320-2.
7. Centers for Disease Control and Prevention. Prevalence
of penicillin-resistant Streptococcal
pneumoniae--Connecticut 1992-1993. MMWR 1994;43:216-7,
223.
8. Advisory Committee for Immunization Practices. Update
on adult immunization: recommendations of the
Immunization Practices Advisory Committee (ACIP). MMWR
1991;40 (RR-12):42-4.



















NEWS AND NOTES

WHONET: An Information System for Monitoring
Antimicrobial Resistance

WHONET is an information system developed to support The
World Health Organization's (WHO) goal of global
surveillance of bacterial resistance to antimicrobial
agents. Microbiologists, clinicians and infection control
workers may use its software to enhance monitoring of
drug resistance in their hospitals and communities and to
merge their files into national, regional, and global
networks for surveillance of drug resistance. WHONET
software can be installed on personal computers and be
configured for the locations of the patients a laboratory
serves and for the antimicrobial agents it tests. The
program accepts susceptibility test results and allows
printing of reports and logbooks and retrieval of data.
If the laboratory already has a computerized reporting
system, a translation program can be created to download
the laboratory's files into WHONET. Either way, the
microbiologists and other infectious disease specialists
gain new analytical tools to monitor and manage
susceptibility test quality and the spread of drug
resistance locally and outside their area.

WHONET can also analyze stored data. From a single
screen, a WHONET user selects the type of analysis to
run, the species of bacteria to analyze, the subsets of
isolates to include (e.g., all, isolates from urine only,
and isolates resistant to gentamicin and from certain
locations), and the antimicrobial agents and period to
examine. Types of analyses include percentage of data
categorized as resistant, intermediate, or susceptible by
standard or other breakpoints; distributions of test
measurements (zone diameter, minimal inhibitory
concentration) in the form of histograms; scatterplots
comparing measurements for different agents or methods
for the same isolates; and line listings of isolates
grouped by combinations of agents to which they are
resistant (antibiotypes) to trace distinctive strains.
Isolates with uncommon antibiotypes can also be flagged
on entry so that they may be rechecked while still
available, and local outbreaks can be detected early.

Although test results are entered and monitored locally
on software configured for local use, they are filed in
a universal file format so that any copy of the program
can analyze the files of any laboratory. This feature has
enabled groups of users in 10 countries to set up passive
surveillance systems by pooling and analyzing their files
collaboratively. WHONET assists such initiatives by
providing file encryption options to ensure
confidentiality before data are pooled and analyzed.

Ongoing local analysis by local workers is the foundation
of the system. It detects local problems in testing,
which no laboratory can avoid entirely, and thus improves
the overall quality of the files. It delineates local
spread of drug-resistant strains, which aids infection
control and can explain and correct uncommon prevalence
of certain types of drug resistance at certain sites. It
allows local workers to distinguish their problems from
those of other sites and focus on infection control or
antimicrobial use that might be related to those
problems.

Expansion of the system has been recommended by the WHO
Scientific Working Group on Monitoring and Management of
Bacterial Resistance to Antimicrobial Agents. For more
information or for participation contact 

Thomas F. O'Brien and John M. Stelling
WHO Collaborating Center for Surveillance of 
Resistance to Antimicrobial Agents
Microbiology, Brigham and Women's Hospital
Boston, MA 02115, USA
tel (1-617) 732-6803
fax (1-617) 732-4144
Internet: whonet@bustoff.bwh.harvard.edu






Recommendations for Preventing the Spread of Vancomycin
Resistance

CDC's Hospital Infection Control Practices Advisory
Committee (HICPAC) has published "Recommendations for
Preventing the Spread of Vancomycin Resistance." The
recommendations focus on vancomycin-resistant enterococci
(VRE).

The reported incidence of infection and colonization with
VRE in U.S. hospitals has increased rapidly in the last
5 years. This increase has compounded the need for
antimicrobial drugs to treat VRE infections. Most VRE are
also resistant to multiple other drugs (e.g.,
aminoglycoside and ampicillin), which have been used for
treating VRE infections. In addition, the possibility
that the vancomycin-resistance genes present in VRE may
be transferred to other gram-positive microorganisms,
especially Staphylococcus aureus, is a serious public
health concern.

Although the epidemiology of VRE has not been fully
elucidated, and most enterococcal infections have been
attributed to the patient's endogenous flora, recent
studies have demonstrated that enterococci, including
VRE, can be spread directly from patient to patient or
indirectly by transient carriage on the hands of
personnel or contaminated environmental surfaces and
patient-care equipment.

In its recommendations, HICPAC stresses that the
prevention and control of vancomycin resistance will
require a coordinated, concerted effort from various
departments of a hospital. Because the recommendations
were developed with limited data and further research is
needed to find cost-effective ways to control the spread
of vancomycin resistance, HICPAC strongly encourages
hospitals to develop their own institution-specific
plans, which should stress the following elements: 1)
prudent vancomycin use by clinicians, 2) education of
hospital staff regarding vancomycin resistance, 3) early
detection and prompt reporting of vancomycin resistance
in enterococci and other gram-positive microorganisms by
the hospital microbiology laboratory, and 4) immediate
implementation of appropriate infection-control measures
to prevent person-to-person transmission of VRE.

The recommendations were developed by HICPAC's
Subcommittee on the Prevention and Control of
Antimicrobial-Resistant Microorganisms in Hospitals and
subject-matter experts and representatives of the
American Hospital Association, American Society for
Microbiology, Association for Professionals in Infection
Control and Epidemiology, Infectious Diseases Society of
America, Society for Healthcare Epidemiology of America,
and Surgical Infection Society. The recommendations were
published in February in Infection Control and Hospital
Epidemiology 1995;16:105-13 and will also be published in
the April 1995 issue of the American Journal for
Infection Control.

Hospital Infection Control 
Practices Advisory Committee
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, Georgia, USA




















Waterborne Cryptosporidiosis Threat Addressed

Cryptosporidium parvum was first recognized as a cause of
human illness in 1976. From 1976 to 1982, the disease was
reported rarely in the United States, primarily among the
immunocompromised. In 1982, the number of reported cases
began to increase dramatically along with the number of
HIV-infected persons; outbreaks among immunocompetent
populations also were reported. Recent municipal
waterborne outbreaks of cryptosporidiosis in Texas
(1984), Georgia (1987), and Oregon (1992), and a massive
outbreak in Wisconsin in 1993 that affected more than
400,000 persons have raised awareness about the
waterborne transmission of cryptosporidiosis. Since 1993,
several smaller cryptosporidiosis outbreaks were reported
in the United States: two were related to drinking water,
six were linked to recreational water, and one was
foodborne.

Cryptosporidiosis is caused by ingestion of the
environmentally tough oocysts of the protozoan parasite
C. parvum, an intracellular organism that can replicate
in the gut epithelial cells of most mammals. Its oocyst
is extremely resistant to chlorine, which is commonly
used to treat municipal water.

In healthy persons, the disease lasts 1 to 2 weeks and
can have considerable economic impact through absenteeism
of those affected. In the immunocompromised, the disease
is often severe, lifelong, and life-threatening. No
effective therapy is available.

The magnitude of the 1993 Wisconsin outbreak and its
association with a municipal water plant operating within
existing state and federal regulations underlined the
need for improved surveillance and coordination among
public health agencies and spurred efforts for regulatory
standards for Cryptosporidium in drinking water. During
1995-1996, the U.S. Environmental Protection Agency (EPA)
intends to implement the Information Collection Rule,
which requires utilities that serve populations of
100,000 or more and use surface water (lakes, rivers,
streams) to test that water routinely for Cryptosporidium
oocysts. If oocysts are found, the utility may also have
to test finished water (tap water). Utilities that serve
populations of 10,000 to 99,000 will also have to test
source water, but for a shorter period. They will not be
required to test tap water, even if oocysts are found.
Authority to issue boil water advisories if oocysts are
found varies from state to state. The health risks from
ingesting low levels of Cryptosporidium are unknown. More
than 300 representatives from 40 states and more than 25
regulatory, public health, water utility, and advocacy
groups met at the Centers for Disease Control and
Prevention (CDC) in Atlanta in September 1994 to discuss
the prevention and control of waterborne
cryptosporidiosis. Recommendations from the CDC workshop
will be published in the next 2 to 3 months.

CDC held the first meeting of the Working Group on
Waterborne Cryptosporidiosis in November 1994. The
working group convenes biweekly by teleconference. For
more information about the group, contact Margaret Hurd
(phone: 404-488-7769, fax: 404-488-7761).

The working group has three main purposes: 1) promote a
regular exchange of ideas, goals, activities, and
proposals among individual scientists, agencies, and
organizations interested in waterborne cryptosporidiosis;
2) make decisions on public health issues related to
waterborne cryptosporidiosis; and 3) assemble smaller,
more focused, task forces with expertise to develop,
implement, and evaluate projects of the working group.

The working group has created task forces to assist
local, state, and national public health departments,
water utilities, and regulatory agencies in preparing for
and managing outbreaks. The task forces have the
following responsibilities:

* Develop and evaluate informational materials about
cryptosporidiosis.
* Develop guidelines on when to initiate or end boil
water advisories.
* Help formulate the language for EPA's Information
Collection Rule.
* Identify officials with authority to issue boil water
advisories. Examine legal issues associated with boil
water advisories and the environmental testing,
surveillance, and diagnostic requirements for waterborne
Cryptosporidium.
 
In addition, technical task forces will collect data to
develop guidelines for persons who may want to use
bottled water and personal-use water filters and provide
updates on the status of environmental sampling, water
testing, and surrogate indicators of Cryptosporidium
oocysts. These task forces will also report on the status
of clinical diagnostic and serologic tools and provide
local cryptosporidiosis infection rates to use in
assessing the risk for waterborne transmission.

C. parvum oocysts are present in most surface water
supplies; better technological tools and epidemiologic
assessments are needed to determine the public health
risks from these oocysts. Until the risks are fully
known, efforts should be made to inform the public about
cryptosporidiosis. Information on opportunistic
infections, including cryptosporidiosis, for physicians
who treat diseases in immunocompromised patients will be
published this fall in a supplement to Clinical
Infectious Diseases by authors from CDC and the
Infectious Diseases Society of America.

Daniel G. Colley
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, Georgia, USA
_____




Editorial Policy and Call for Articles

The goals of Emerging Infectious Diseases (EID) are to
promote the recognition of new and reemerging infectious
diseases and to improve the understanding of factors
involved in disease emergence, prevention, and
elimination. EID has an international scope and is
intended for professionals in infectious diseases and
related sciences. We welcome contributions from
infectious disease specialists in academia, industry,
clinical practice, and public health as well as from
specialists in economics, demography, sociology, and
other disciplines whose study elucidates the factors
influencing the emergence of infectious diseases.

EID will be published in English and will feature three
types of articles: Perspectives, Synopses, and
Dispatches. The purpose and requirements of each type of
article are described in detail below.


Instructions to Authors

Editorial Material: Manuscripts should be prepared
according to the "Uniform Requirements for Manuscripts
Submitted to Biomedical Journals" (JAMA 1993:269[17]:
2282-6).

Begin each of the following sections on a new page and in
this order: title page, abstract, text, acknowledgments,
references, each table, figure legends, and figures. On
the title page, give complete information about each
author (full names and highest degree). Give current
mailing address for correspondence (include fax number
and e-mail address). Follow Uniform Requirements style
for references. Consult List of Journals Indexed in Index
Medicus for accepted journal abbreviations. Tables and
figures should be numbered separately (each beginning
with 1) in the order of mention in the text. Double-space
everything, including the title page, abstract,
references, tables, and figure legends. Italicize
scientific names of organisms from species name all the
way up, except for vernacular names (viruses that have
not really been speciated, such as coxsackievirus and
hepatitis B; bacterial organisms, such as pseudomonads,
salmonellae, and brucellae). 

Perspectives: Contributions to the Perspectives section
should address factors known to influence the emergence
of infectious diseases, including microbial adaption and
change; human demographics and behavior; technology and
industry; economic development and land use;
international travel and commerce; and the breakdown of
public health measures. Articles should be approximately
3,500 words and should include references, not to exceed
40. The section should begin with an introduction
outlining the relationship of the issues discussed in the
paper to the emergence of infectious diseases. Use of
additional subheadings in the main body of the text is
recommended. If detailed methods are included, a separate
section on experimental procedures should immediately
follow the body of the text. Photographs and
illustrations are optional. Provide a short abstract (150
words) and a brief biographical sketch.

Synopses: Submit concise reviews of infectious diseases
or closely related topics. Preference will be given to
reviews of new and emerging diseases; however, timely
updates of other diseases or topics are also welcome.
Synopses should be approximately 3,500 words and should
include references, not to exceed 40. The section should
begin with an introduction outlining the relationship of
the issues discussed in the paper to the emergence of
infectious diseases. Use of additional subheadings in the
main body of the text is recommended. If detailed methods
are included, a separate section on experimental
procedures should immediately follow the body of the
text. Photographs and illustrations are optional. Provide
a short abstract (150 words) and a brief biographical
sketch.

Dispatches: Provide brief updates on trends in infectious
diseases or infectious disease research. Dispatches
(1,000 to 1,500 words of text) should not be divided into
sections. Dispatches should begin with a brief
introductory statement about the relationship of the
topic to the emergence of infectious diseases. Provide
references, not to exceed 10; and figures or
illustrations, not to exceed two.

All articles will be reviewed by independent reviewers.
The Editor reserves the right to edit articles for
clarity and to modify the format to fit the publication
style of Emerging Infectious Diseases.

Send documents in hardcopy (Courier 10-point font), on
diskette, or by e-mail. Acceptable electronic formats for
text are ASCII, WordPerfect, AmiPro, DisplayWrite,
MS Word, MultiMate, Office Writer, WordStar, or Xywrite.
Send graphics documents in Corel Draw, Harvard Graphics,
Freelance, .TIF (TIFF), .GIF (CompuServe), .WMF (Windows
Metafile), .EPS (Encapsulated Postscript), or .CGM
(Computer Graphics Metafile). The preferred font for
graphics files is Helvetica. If possible, convert
Macintosh files into one of the suggested formats. Submit
photographs in camera-ready hardcopy.

Send all manuscripts and correspondence to the Editor,
Emerging Infectious Diseases, National Center for
Infectious Diseases, Centers for Disease Control and
Prevention, 1600 Clifton Road, Mailstop C-12, Atlanta, GA 
30333,USA, or by e-mail on the Internet to
eideditor@cidod1.em.cdc.gov.