With the invention of the microscope it was finally possible to see the microorganisms and scientists started understanding the link between microorganisms and disease (see Germ Theory of Disease in Chapter 1, Scope of Microbiology). Soon thereafter hand washing (Semmelweis) and antiseptic methods (Lister) were used in many hospitals, to control the spread of disease. The breakthrough of vaccination against smallpox (Jenner) and the discovery of penicillin (Fleming) further helped the battle against infectious diseases.

IMPACT

After the discovery of penicillin, production methods were further developed, allowing large quantities of penicillin to be produced. By the end of World War II, enough penicillin was produced to treat 7 million patients a year. The golden age of antibiotics dawned with considerable achievements in the discovery and development of many different types of antibacterial drugs (see Chapter 22, Antimicrobial Drugs). Because of the success of these drugs the fight against bacteria seemed to have been won. It was reported that in 1967 and 1969, the U.S. Surgeon General, William H. Stewart, commented that we had essentially defeated infectious diseases and “we could close the book on infectious disease.” During the same time frame, many pharmaceutical companies shifted their main priorities to drug development for chronic disease therapy and less to the development of new antibacterials. Unfortunately, microbial evolution has not stopped and many microbes, not only bacteria, have developed resistance to the currently available drug treatments. The incidence of multidrug-resistant pathogenic bacteria is on the rise.

FUTURE

Emerging and reemerging infectious diseases are on the rise because of globalization, urbanization, multidrug resistance, and many other factors. This is a global problem and new and advanced international surveillance methods have been developed. The World Health Organization is constantly striving to improve prevention and control methods. Furthermore, pharmaceutical companies, especially biotechnology-oriented ones, are actively pursuing the development of new antimicrobial drugs. Infectious diseases have emerged throughout history and new infections continue to emerge today, and most likely will continue to do so in the future.

Introduction

Emerging infectious diseases are diseases that are newly identified in a population, or that have existed but have changed. They show an increase in incidence, currently or in the recent past, or have a potential to increase in the near future. Emerging diseases can be caused by viruses, bacteria, fungi, protozoans, or helminths. Older diseases that have been known for a long time and were previously under control, but are recurring, are called reemerging infectious diseases.

Emerging/Reemerging Infectious Diseases

The increasing international threat of infectious diseases has received special attention in the past few decades. The emergence of infectious diseases generally involves two steps:

1. The introduction of the pathogen into a new host population, and

2. The establishment and further spreading of the pathogen within the new host population, a process referred to as adoption.

The occurrence of a new infectious disease often seems strange; however, there are specific factors that are generally responsible for such emergence. Although some infectious diseases have been successfully controlled by modern technology, new emerging infectious diseases such as HIV/AIDS, severe acute respiratory syndrome (SARS), and West Nile virus and Ebola infections are continually appearing and are on the rise. In addition, other infectious diseases including malaria, tuberculosis, and bacterial pneumonias are reappearing in strains that are resistant to antimicrobial drug treatments.

Factors of Emergence/Reemergence

Factors responsible for the emergence of new infectious diseases include human demographics and behavior, ecological changes and agricultural development, international travel and commerce, technology and industry, microbial adaptation and change, breakdown of public health measures, human susceptibility to infection, climate and weather, economic development and land use, war and starvation, and intent to harm.

Human Demographics and Behavior

Changes in human demographics due to migration or war are often significant factors in the emergence of infectious diseases. Population movements are often due to economic conditions, which encourage workers to move from rural areas into cities. Beginning in the twentieth century a rapid urbanization of the world’s population occurred: whereas in 1950, 29% of the population lived in urban areas, the United Nations estimates that in 2030 approximately 60% will live in urban areas, increasing to more than 69% by the year 2050 (Figure 18.1 and Table 18.1). The population density in urban areas makes disease transmission easier as it allows infections that arise in isolated rural areas that previously remained vague and localized, to reach the larger urban population. Once in the city, the disease not only spreads locally, but can also spread farther by intraurban transport routes, along highways, and by airplane.

TABLE 18.1

Urban and Rural Population Percentages from 1950 to 2050

Year	Percent Urban
Percent Urban Population from 1950 to 2050
1950	29.1
1960	32.9
1970	36.0
1980	39.1
1990	43.0
2000	46.6
2010	50.6
2020	54.9
2030	59.7
2040	64.7
2050	69.6

Year	Percent Rural
Percent Rural Population from 1950 to 2050
1950	70.9
1960	67.1
1970	64.0
1980	60.9
1990	57.0
2000	53.4
2010	49.4
2020	45.1
2030	40.3
2040	35.3
2050	30.4

FIGURE 18.1 Urban and rural world population from 1950 to 2030.

Human behavior, especially in large population centers, can have important effects on disease dissemination. Well-known examples include sexually transmitted infections, and intravenous drug use, which have contributed to the emergence and spread of HIV/AIDS and hepatitis.

Child care centers have become a way of life especially in many civilized countries, including the United States. According to the U.S. Food and Drug Administration (FDA) more than half of all mothers with young children have jobs outside the home and day care centers provide a necessary service. Unfortunately, this also provides a focal point for certain infectious diseases that can easily spread in the center, and also into the community.

Another factor in the emergence and transmission of infectious disease is the increasing age of the human population, largely due to medical advances. Many persons with advanced age or a chronic condition will have a compromised immune system, resulting in greater susceptibility to disease. Opportunistic organisms will then have the chance to develop an infection that normally would be prevented by an intact immune system. Once the disease has developed in an immunocompromised host, it can spread further into the community.

Ecological Changes and Agricultural Development

Changes in the ecosystem are frequently identified as factors increasing the occurrence of emerging infectious diseases. These ecological changes include changes in agricultural practices, economic development, and changes in land uses. Once the ecosystem is disturbed, outbreaks of previously unrecognized diseases occur and these often turn out to be of a zoonotic nature. Ecological changes often place people in contact with a natural reservoir or host that is unfamiliar to the population moving into the changed habitat. The building of dams and deforestation or reforestation are changes in the ecological makeup that will influence waterborne and vector-borne disease transmission. The movement of people into these areas will expose a larger population to wild animals and potential disease vectors. Agricultural development and urban development are the most common ways by which society alters the environment and introduces the population to previously unknown microbial challenges.

International Travel and Commerce

Persons infected with an exotic disease anywhere in the world can readily travel to any major city, including those in the United States. Even in the sixteenth and seventeenth centuries ships bringing slaves from West Africa to the New World also brought along infectious diseases, such as yellow fever and its mosquito vector. Other examples include the import of a filovirus into Marburg, Germany in 1967, with a shipment of African green monkeys used for laboratory purposes. The virus spread from the primate host to some of the human handlers, and subsequently to staff taking care of the infected people. This virus is now called the Marburg virus, which was responsible for seven deaths during that first outbreak. More outbreaks due to this virus occurred in many countries, including Angola in 2005. The mosquito-borne disease malaria is one of the most frequently imported diseases into nonendemic areas. The sporadic Ebola outbreaks in Central Africa could potentially be spread via air travel throughout the world within a matter of days.

Foods from other countries that are routinely imported, and vectors hitchhiking on imported products, also represent a potential for emerging infectious diseases all around the world. Cruise ships are also a great environment for emerging diseases, because the passengers are frequently exposed to new environments, and live in a high population density.

LIFE APPLICATION

Pathogenic Hitchhikers: It’s a Small World After All

In the 1960s the Surgeon General of the United States acknowledged that the time was at hand when we could “close the book on infectious disease”. As a result of improvements of public health programs, hygiene, and advances in the development of new drugs and vaccines to combat infectious diseases, many public health officials stated that, at least in the Western world, death due to infectious diseases had been virtually eliminated. Unfortunately, this has not been the case as recent worldwide problems exist, with diseases such as malaria, West Nile virus, dengue fever, and SARS still spreading and claiming victims. There are a number of factors that contribute to the successful spread of pathogens to new host populations, but one that has changed considerably over the past century is the spread of disease through international travel and commerce. For instance, increases in cases of yellow fever in Africa have raised some serious concern in the international community regarding the potential epidemic should the virus and insect vector come together on a wide scale. There is fear that the virus, which is now confined mostly to the savannah and forest areas, may be transported to more urban areas as a result of migration due to economic development policies. If the virus is introduced to the mosquito vector in the urban environment, officials fear it could give rise to an urban epidemic. Air travel and transport shipping could then bring the virus to the United States, where the mosquito insect vector is already well established in the southern states. Once again, when the virus and vector are brought together, the potential for a devastating epidemic could arise. Although virtually any form of international transportation has the potential to transport a disease vector, the form that has historically proven to be most effective at spreading pathogens worldwide has been ship transport. The shipboard environment and the equipment and containers being transported favor the survival of animal vectors, with the bacterial/viral pathogens safely hitchhiking on or in their bodies.

Technology and Industry

Technical and industrial advancements in both the food and healthcare industries generally have a positive impact on the quality of life; however, they can also bring about the spread of infectious disease. Modern production methods tend to increase efficiency and reduce costs, but unfortunately also increase the chances of accidental contamination. This particular problem is amplified by globalization, because of the opportunity to introduce microbes from different parts of the world. In bulk processing, a microbe present in raw material may end up in a large batch of the final product.

At present animal feed ingredients include rendered animal products, animal wastes, antibiotics, metals, and fats, all of which increase the potential for higher levels of bacteria, antibiotic-resistant bacteria, prions, and dioxin-like compounds in animals. Animal food products are then intended for human consumption. Although the FDA does closely monitor these practices, accidental outbreaks of old or emerging infections do occur.

Many technological advances have been made in healthcare during the twentieth century, yet there has been a dramatic increase in nosocomial infections (see Chapter 9, Infection and Disease), often due to the development of antibiotic resistance in microbes.

Microbial Adaptation and Change

Like other organisms microbes are constantly evolving, but at a much faster rate because of their rapid reproduction/generation cycles. Microbes, especially bacteria and viruses, can also adapt quickly to adverse environments and this change is a major contributing factor to the emergence of “new” pathogens. Almost all RNA viruses, such as influenza, HIV, and hemorrhagic fever viruses, undergo frequent and unpredictable genetic mutations. Microbes have enormous evolutionary potential as they are able to undergo changes in pathogenicity, as well as often being able to avoid the immune system of the host. Their capacity to adapt to new environments is often enhanced by human activities.

Antimicrobial resistance (see Chapter 22, Antimicrobial Drugs) due to the overuse of antimicrobial drugs and the failure to ensure proper diagnosis and adherence to treatment has become a significant public health problem. This widespread use of antibiotics and other antimicrobials has resulted in evolutionary adaptations in microbes, enabling them to survive many powerful drugs. Antimicrobial drug–resistant strains are a continuing source of emerging infections and diseases.

MEDICAL HIGHLIGHTS

Antigenic Drift: “Putting on a New Coat”

RNA viruses such as the influenza viruses can change in two different ways. One way is referred to as antigenic drift, the other as antigenic shift, and one should not be mistaken for the other. An antigenic shift is a process involving at least two different strains of viruses, or even different viruses, combining to form a new virus that may then infect different species (i.e. a new strain of the avian flu virus infecting humans).

In an antigenic drift there are small changes in the viral coat (surface proteins) that happen over time. An antigenic drift can produce a new influenza virus strain that may not be recognized by the body’s immune system. For example, the virus may put on a new coat, and antibodies produced earlier, due to an infection or vaccination (flu vaccination) are no longer effective against the new strain. This is one of the reasons why people can get the flu more than one time. The flu vaccine contains three virus strains (one virus with three different “coats”), and one or two of the three strains are usually updated each year to keep up with the changes in the circulating flu viruses. People who need to or want to be protected from the flu need to get an annual flu shot.

LIFE APPLICATION

Mosquito Bites: “Fight the Bite” (CDC)

The West Nile virus is an infectious disease that first appeared in the United States in 1999. It is a known virus that has been introduced into a new geographical territory, and as of 2007 human cases have been reported in almost all states of the United States. The virus is spread by infected mosquitoes. People infected with the virus generally show mild or no symptoms at all; however, if the virus enters the brain it can be deadly. The “fight the bite” call by the CDC emphasizes the following (http://www.cdc.gov/ncidod/dvbid/westnile/index.htm):

• Avoid mosquito bites

• Use insect repellent

• Be aware of peak mosquito hours

• Drain all standing water

• Install or repair screens

Furthermore, report dead birds to local authorities, as this may be a sign that the virus is circulating between birds and mosquitoes in an area. More than 130 species of birds are known to have been infected with the West Nile virus. It is important to note that all infected birds die from the virus; however, one should not assume that every dead bird is a victim of this virus.

MEDICAL HIGHLIGHT

H1N1: Return of a Killer

In 1918, Influenza A virus subtype H1N1 swept across the world and killed 50–100 million people worldwide. The particular strain of H1N1 that caused this pandemic is often referred to as avian flu, as this specific strain is endemic in birds. In 1976, 1988, 1998, and in 2007 there were minor outbreaks of a flu caused by another strain of H1N1 endemic to pigs, and it was thus referred to as swine flu. In 2009 a new strain of the H1N1 subtype returned, but this time it has a very different genetic makeup. Six genes isolated from cases of the flu in America have been found to be mixtures of swine, avian, and human influenza viruses. Due to this unique mix of genes, there is a serious concern among many health agencies that the existing stocks of vaccines for the “old” strains of H1N1 will not be very effective against this new strain. Recently identified as a full-scale pandemic, the spread of the new H1N1 subtype is being carefully tracked by the WHO. As of June 2009, 74 countries have reported cases of influenza A(H1N1), with more than 27,000 infected and over 150 deaths. It is apparent that this new strain will present a challenge to health organizations everywhere, and its future effects on the world health situation are at this time unknown.

The National Institute of Allergy and Infectious Diseases (NIAID) has classified emerging and reemerging infectious diseases into only three groups:

• Group I: Pathogens that have been newly recognized in the past two decades

• Group II: Reemerging pathogens

• Group III: Agents with bioterrorism potential, subdivided into categories A, B, and C (see Chapter 24, Microorganisms in the Environment and Environmental Safety). Only NIAID category A organisms are included in the tables of this chapter

Bacterial, viral, fungal, protozoan, as well as prion-related emerging diseases are included in these groups (Tables 18.2 through 18.5). According to the Centers for Disease Control and Prevention (CDC, Atlanta, GA), almost 70% of emerging infectious disease episodes in the last decade or more have been zoonotic diseases. The recurrent examples of infections originating as zoonoses suggest that this reservoir of infections is a potentially rich source of emerging diseases and the periodic appearance of new zoonoses indicates that this pool is not exhausted. Although zoonotic agents generally do not spread easily from person to person, other factors, as discussed previously, might help to transmit the infection.

TABLE 18.2

Bacterial Emerging and Reemerging Infectious Diseases

Disease	Organism	Category	Transmission
Anthrax (Chapters 9, 11, and 24)	Bacillus anthracis	Group III	Cutaneous, inhalation, gastrointestinal
Cat scratch disease	Bartonella henselae	Group I	Cat bite or scratch, but recently tick-borne and transmitted
Lyme borreliosis (Chapter 9)	Borrelia burgdorferi	Group I	Tick
Botulism (Chapters 9, 12, and 13)	Clostridium botulinum	Group III	Four types: foodborne, infant, wound, undetermined
Pseudomembranous colitis	Clostridium difficile	Group II	Fecal–oral route
Ehrlichiosis (Chapter 9)	Ehrlichia spp.	Group I	Lone star tick (Amblyomma americanum)
Tularemia	Francisella tularensis	Group III	Tick, deerfly, other insect; handling infected animal carcasses; contaminated food or water; inhalation
Peptic ulcer (Chapter 12)	Helicobacter pylori	Group I	Fecal–oral; kissing
MRSA infections (Chapter 22)	Staphylococcus aureus	Group II	Usually nosocomial, but also community acquired
Group A streptococcal disease (GAS) (Chapter 11)	Streptococcus, group A	Group II	Direct contact with nasal or pharyngeal mucus from infected persons; contact with infected wounds or sores of the skin
Plague (Chapter 24)	Yersinia pestis	Group III	Flea bites

MRSA, Methicillin-resistant Staphylococcus aureus.

TABLE 18.3

Viral Emerging and Reemerging Infectious Diseases

Disease	Organism	Category	Transmission
ABL infection (Chapters 7 and 9)	Australian bat lyssavirus	Group I	Scratch or bite from infected bat
Neurological disease, hand, foot and mouth disease	Enterovirus 71	Group II	Fecal-oral, some indications of respiratory transmission
Respiratory illness (Chapter 7)	Hendra virus (equine morbillivirus)	Group I	Flying foxes (Australia)
Hepatitis (Chapters 9 and 12)	Hepatitis C virus	Group I	Blood-borne
Hepatitis (Chapters 9 and 12 )	Hepatitis E virus	Group I	Contaminated food or water
Discovered in Kaposi’s sarcoma (Chapter 7)	Human herpesvirus 8	Group I	Not established
Associated with roseola (Chapters 7 and 10)	Human herpesvirus 6	Group I	Opportunistic
“Fifth disease” (Chapters 7 and 9)	Human parvovirus B19	Group I	Person-to-person contact, or direct contact with saliva, sputum, or nasal secretion of infected person
Mumps (Chapters 7, 9, and 11)	Mumps virus	Group II	Person to person by saliva droplets or direct contact with contaminated articles
Smallpox (Chapters 10 and 24)	Variola virus	Group III	Person to person, infected aerosols, face-to-face contact with infected person after fever has begun
Viral hemorrhagic fevers (Chapter 24)	Arenaviruses Bunyaviruses Flaviruses Filoviruses

Group III Zoonotic with exception of the filovirus (can also be transmitted from person to person)

ABL, Australian bat lyssavirus.

TABLE 18.4

Fungal Emerging and Reemerging Infectious Diseases

Disease	Organism	Category	Transmission
Coccidioidomycosis	Coccidioides immitis	Group II	Inhalation of the conidia
Human microsporidiosis	Encephalitozoon cuniculi Encephalitozoon hellem Encephalitozoon intestinalis	Group I	Zoonotic and environmental (spores on water surface)

TABLE 18.5

Protozoan Emerging and Reemerging Infectious Diseases

Disease	Organism	Category	Transmission
Acanthamebiasis	Acanthamoeba	Group I	Contact lenses; through skin
Babesiosis (Chapter 8)	Babesia spp.	Group I	Bite of Ixodes tick

Addressing and Preventing Emerging and Reemerging Diseases

Many infectious diseases that occur in the United States are in the category of Nationally Notifiable Diseases (see Box 9-1 in Chapter 9, Infection and Disease). In other words, they need to be reported to the public health system. Numerous other emerging diseases are not yet in this reportable category because of continuous changes and the need for constant updates. General provisions for fighting infectious diseases in the United States include the responsibilities for monitoring, preventing, and controlling infectious disease. These responsibilities are carried out by hospitals, clinical laboratories, pharmaceutical companies, healthcare providers, universities, and various other research groups. Although these are part of a large system working to reduce the impact of pathogenic organisms, it is the CDC that acts as the lead U.S. federal agency responsible for providing information, recommendations, and technical assistance to support state and local public health departments (see Epidemiology and Public Health in Chapter 9, Infection and Disease).

Surveillance

In the United States, surveillance of infectious diseases, including new and reemerging ones, includes efforts at the state and federal levels. State departments collect and analyze data on infectious disease cases that were reported to the departments by healthcare providers. The reported cases are then verified by the state public health departments, which in turn report the information to the CDC. At the federal level, agencies and departments collect and analyze disease surveillance data and maintain the disease surveillance systems.

The first step in disease detection involves surveillance to determine whether clinical symptoms associated with a particular incident warrant intensive public health attention. These may include the following:

• Acute respiratory disease

• Unusual clustering of disease or deaths

• Resistance to common drug treatments

An epidemic is often detected through routine surveillance or through an unusual cluster of cases recognized by a healthcare provider. Examples of such cases are the hantavirus outbreak in 1993 in the American Southwest, or the presence of the West Nile virus in the western hemisphere. Consequently, new infectious diseases are recognized mainly because of incidences of an actual epidemic.

Investigation

One of the most important reasons to investigate an outbreak of infectious disease, regardless of whether it is a newly emerging or reemerging disease, is that exposure to the source of infection may be continuing. Quick and precise identification of the pathogen, its transmission, and an appropriate response may be necessary to prevent additional cases of a potentially dangerous disease. In general, once a decision has been made to investigate an outbreak the following activities are involved:

• Epidemiologic investigation (see Chapter 9, Infection and Disease)

• Environmental investigation

• Interaction with the public

Even if an investigation is done after an outbreak it may still be important in order to prevent other outbreaks, describe new disease, evaluate existing prevention strategies, and address public concerns about the outbreak. Again, the CDC supports state and local health officials in this effort and the CDC’s National Center for Preparedness, Detection, and Control of Infectious Diseases (NCPDCID) provides public health laboratories with reliable microbiological references and reagents that may not be available commercially.

Response

The intervention/prevention/response to emerging diseases will depend on the disease and should be a public health response utilizing a variety of methods. One of the most successful tools in preventing infectious diseases is appropriate immunization programs. The National Immunization Program supports local health departments in planning, developing, and implementing immunization programs (http://www.cdc.gov/vaccines/). Other measures to prevent or interrupt the transmission process of infectious agents include rodent or insect vector control, food recall, isolation, and quarantine. Because human behavior is an important factor in infectious disease transmission, education and information campaigns are also an essential feature of most disease response activities.

Global Concerns

One of the roles of the Centers for Disease Control and Prevention (CDC) is to protect people in the United States from infectious disease. Yet, the health of a nation cannot be sufficiently protected without addressing infectious disease problems that occur elsewhere in the world. Because of expanding air travel and international trade, infectious microbes can be easily transported across borders on a daily basis. Microbes can be carried by infected people, animals, and insects. In addition, commercial shipments can contain contaminated materials, such as food.

The National Center for Infectious Diseases (NCID), a branch of the CDC, has now been officially reorganized. The former divisions and programs of the NCID have been reorganized into multiple national centers. The National Center for Preparedness, Detection, and Control of Infectious Diseases (NCPDCID) is now the agency responsible for the protection of domestic and international populations. Through their leadership, partnership, epidemiologic and laboratory studies, and the use of quality systems, this agency establishes standards and practices for response to infectious diseases (http://www.cdc.gov/ncpdcid/).

The International Emerging Infections Program (IEIP) is an integral component of the CDC’s Global Disease Detection Program. This is the agency’s principal program to reinforce the identification of emerging infections around the world, and to effectively respond to them (http://www.cdc.gov/ieip/).

U.S. Global Public Health

According to the CDC the United States should continue to increase its participation in combating all infectious disease threats around the world. These include the following:

• Protecting the health of U.S. citizens at home and abroad by controlling disease outbreaks and also dangerous endemic diseases. Wherever endemic diseases occur, the disease must be prevented from spreading internationally.

• Furthering U.S. humanitarian efforts potentially saves many human lives by preventing infectious diseases overseas. The prevention of many infectious diseases can be achieved by vaccination.

• Providing diplomatic and economic benefits for international projects that address infectious diseases. Improvements in global health will not only enhance the economy but also reduce U.S. healthcare costs by decreasing the number of imported diseases.

• Enhancing security to prevent the intentional release of biological agents by terrorist organizations (see Bioterrorism in Chapter 24, Microorganisms in the Environment and Environmental Safety).

Furthermore, in consultation with global public health partners the CDC defines global infectious disease priorities in six areas:

1. International outbreak assistance is considered to be an integral function of the CDC. This needs to include follow-up assistance after each acute emergency response to maintain control of new pathogens after the outbreak.

2. A global approach to disease surveillance needs to evolve into a global “network of networks” to provide early warning of emerging health threats. Such a network also increases the capacity to monitor the effectiveness of public health control measures.

3. Applied research on diseases of global importance, including those that are uncommon in the United States, is a valuable resource because of the dangers represented by certain imported diseases.

4. Applications of proven public health tools need to be identified and shared with the international community.

5. Global initiatives for disease control are needed to reduce the prevalence of HIV/AIDS in young people by 25% and to reduce deaths from tuberculosis and malaria by 50% by the year 2010. To reduce infant mortality the CDC shall work with the Global Alliance for Vaccines and Immunization to enhance delivery and use of new vaccines against respiratory illnesses and other childhood diseases.

6. Public health training through the encouragement and support of the CDC should result in the establishment of International Emerging Infections Programs (IEIPs) in developing countries. These centers of excellence will integrate disease surveillance, applied research, prevention, and control activities.

Global Surveillance

In industrialized countries communicable disease mortality has significantly decreased over the past century. Health agencies in these countries are concerned mostly with preventing diseases from entering the country and causing an outbreak or reemergence. Developing countries are concerned with the early detection of communicable disease outbreaks; and stopping their mortality, spread, and potential impact on trade and tourism.

To rapidly identify and contain public health emergencies the world requires a reliable global system. The International Health Regulations (IHR), revised in 2005, provide such a global framework to address these needs through a collective approach for prevention, detection, and timely response to any public health emergency of international concern. Once a communicable disease outbreak has been confirmed, the information is posted on the World Wide Web, and is accessible by healthcare professionals and the general public (http://www.who.int/csr/don/en/). The international response to an outbreak involves a World Health Organization (WHO) team that arrives on site within 24 hours of the information release, for initial assessment and the beginning of immediate control measures. The international response linked to the global surveillance presents a worldwide “network of networks,” available for technical or humanitarian support, ensuring that no one country has to bear the entire burden.

HEALTHCARE APPLICATION
Examples of Epidemic and Pandemic Alert and Response *

Date	Disease	Location	Comments
April 30, 2008	Avian influenza	Situation in Indonesia	New case of human infection of H5N1 avian influenza: 3-yr-old male
April 25, 2008	Yellow fever	Liberia	30-yr-old male, same community as index case; two confirmed cases, one death
April 22, 2008	Severe acute watery diarrhea with Vibrio cholerae–positive cases	Vietnam	2490 cases between March 5 and April 22, 377 cases positive for V. cholerae
April 18, 2008	Rift Valley fever	Madagascar	418 suspected cases, including 17 deaths
April 17, 2008	Avian influenza	Egypt	Update 10: New case, 2-yr-old male