Globalization presents new challenges and opportunities in combating diseases likely to cause epidemics.
As a result of increased international travel and trade, local events acquire international importance. At the same
time, the rapid global expansion of telecommunications and broadened access to news media and the Internet have
changed the way society treats information. Reports of disease outbreaks are more widely disseminated and more
easily accessible than ever before. However, the quality of information is no longer controlled and may be provided
out of context, often causing unnecessary public anxiety and confusion. Rumors that later prove to be
unsubstantiated may lead to inappropriate response, causing disruption in travel and trade and economic loss to
The World Health Organization (WHO), speaking for 191 member countries, is uniquely positioned to
coordinate infectious disease surveillance and response at the global level. WHO receives reports of disease
outbreaks around the world from various sources. While some of these reports are warnings of genuine epidemics,
others may reflect endemic disease or may be mere rumors.
To investigate and follow up outbreak reports, WHO established an innovative mechanism--outbreak
verification--in early 1997. Outbreak verification is a new approach to global disease surveillance
(1). Its aim is to
improve epidemic disease control by informing key public health professionals about confirmed and unconfirmed
outbreaks of international public health importance.
The Outbreak Verification System
The outbreak verification system follows the general principles of surveillance: systematic collection,
collation, analysis, and interpretation of data and dissemination to those who need the information for action
Data derived from an extensive network of information sources are transformed by the outbreak
verification team into timely, accurate information about important disease outbreaks.
When the outbreak verification team receives an unconfirmed outbreak report, the relevance to
international public health is assessed, and, if appropriate, further information is sought. Once an outbreak is
substantiated and considered of public health importance, information is rapidly disseminated to a network of
Sources of Information
Outbreak verification is based on a broad range of information sources, including national institutes of
public health, WHO offices at regional and national level, the United Nations system, nongovernmental
organizations, WHO collaborating centers, newspapers, television, and radio . With the advent of modern
communication technologies, many initial outbreak reports now originate in the electronic media and electronic
discussion groups. Indeed, the abundance of outbreak-related documents on the World Wide Web presents a
challenge: identifying reports of global public health importance.
The tasks of identifying and extracting outbreak reports from the electronic media is mainly performed by
the Global Public Health Information Network (GPHIN), an electronic surveillance system developed by Health
Canada. GPHIN continuously monitors some 600 sources, including all major news wires, newspapers, and
biomedical journals. The system focuses its search on communicable diseases but will soon also cover
noncommunicable diseases, food and water safety, environmental health risks, and the health impact of natural
disasters. The quality of reports retrieved by GPHIN varies considerably, and information may be presented out
Other information providers are the Internet and electronic-mail-based discussion groups. Their scope and
readership may be worldwide (e.g., ProMed), regional (e.g., PACNET in the Pacific region), or specific (e.g.,
TravelMed). These groups can be accessed through free and unrestricted subscription. Because they receive
outbreak information from many sources, including sources other than the electronic media, they are valuable
Selection of Outbreak Reports for Verification
The verification team first determines if an event is of potential international public health importance.
International public health importance has been defined as serious health impact or unexpectedly high rates of
illness and death; potential for spread beyond national borders; interference with international travel or trade; or
likely need for international assistance in disease control.
Each event is assessed individually on the basis of these criteria. While some diseases will almost always
be regarded important for international public health (e.g., Ebola hemorrhagic fever, cholera), others may not,
depending on the circumstances.
Process of Verification
Once an event has been assessed as of potential international importance, the process of verification is
The outbreak verification team establishes the potential importance of the event, on the basis of available
background information, endemicity levels, and details of previous outbreaks. This information is then shared by e-mail with designated contacts in WHO regional offices, who seek confirmation of details from health authorities in
the countries concerned, usually through the WHO representative. The outbreak verification team may seek
additional information from other organizations in the field, such as the International Red Cross, Médecins sans
Frontières, and Medical Emergency Relief International.
Upon receipt of feedback, the outbreak verification team determines if the event meets the definition of an
outbreak (observed number of cases exceeds expected number of cases in a given population for a given period) and
the criteria for international public health importance. Reaching a final decision may require further consultation
with the WHO regional office or the country representative or health authorities in-country.
Dissemination of Information
Timely dissemination of outbreak information to those who need to know is a key aspect of the outbreak
verification process, and details of outbreaks with potential for international public health importance are
disseminated through various channels. Information is shared directly with partners for immediate action
(epidemic response) but also routinely with a wider audience through the Outbreak Verification List, the WHO
Disease Outbreak News on the World Wide Web, and the Weekly Epidemiological Record (WER).
The Outbreak Verification List is distributed weekly by e-mail to approximately 800 subscribers. The
distribution list includes WHO staff worldwide, other UN agencies, national health authorities, field epidemiology
training programs, and nongovernmental organizations. Because the Outbreak Verification List is not an official
WHO publication, its distribution is limited to subscribers.
The WHO Disease Outbreak News is on the WHO web page and provides the public with information
about outbreaks of international importance. Often events that initially appeared in the Outbreak Verification List
are subsequently reported in Outbreak News. Because Outbreak News is in the public domain, only information
about officially confirmed outbreaks is disseminated. Outbreak News
(http://www.who.int/emc/outbreak_news/index.html) is one of the most frequently accessed sites on the WHO
The third mechanism for communicating outbreak-related information is the
WER. This report is
published in French and English and issued in print and electronically (http://www.who.int/wer/index.html). It
covers epidemiologic information on cases and outbreaks of diseases under the International Health Regulations
(yellow fever, plague, cholera) and also on other communicable diseases of public health importance. Recently, an
Outbreak News section mirroring the Outbreak News on the web page has been added to the
Coordination of timely and effective epidemic response is intrinsically linked to dissemination of
information about important disease outbreaks. During the verification process, WHO routinely offers technical
assistance for the investigation and control of the event. Such assistance may range from advice (e.g., identifying
appropriate laboratory facilities) to deployment of field teams. WHO coordinates the deployment of field teams,
drawing from within WHO and among collaborating centers and other international partners.
Effectiveness of Outbreak Verification
From July 1, 1997, to July 1, 1999, the outbreak verification team identified 246 outbreak reports of
potential importance for world health and disseminated them in the Outbreak Verification List. Of the 246
outbreaks, 43% occurred in the African region of WHO; 12% each in the regions of the Americas, eastern
Mediterranean, and Europe; 11% in the Southeast Asian region; and 9% in the Western Pacific region. Countries
subject to complex emergencies were involved in 121 (49%) outbreaks and industrialized countries in 6 (2%)
The most common diseases or syndromes disseminated in the Outbreak Verification List were cholera (n
= 78), acute hemorrhagic fevers (n = 24), and acute diarrheal diseases (n = 22). In two (0.8%) cases, the Outbreak
Verification List disseminated information about events that could not be substantiated later. Seventy-one percent of the initial reports were retrieved from informal or unofficial sources (e.g., the media, electronic
discussion groups, nongovernmental organizations), and 29% were provided by official sources (e.g., WHO
network, Ministries of Health). Unofficial sources were the most frequent providers of initial information in all
WHO regions and for all diseases, including those subject to the International Health Regulations (cholera, plague,
Information about the date of onset of an outbreak was available in 134 (55%) cases. The median time
between reported onset of an outbreak and the outbreak verification team's receipt of the first report was 18 days
(from 1 to 215 days). This interval was similar for official and unofficial sources but varied considerably for
different diseases: 13 to 15 days (median) for acute hemorrhagic fevers, anthrax, and cholera; 20 to 35 days
(median) for yellow fever and plague; and >50 days (median) for acute respiratory syndrome and meningococcal
disease. Most reports were verified within a few days and important events usually within <48 hours. The median
time between receipt of a first report and appearance of the event in the weekly Outbreak Verification List was 3
days (0 to 69 days).
In addition to the 246 disseminated outbreak reports, 69 events were verified from July 1, 1997, to July 1,
1999, but were not reported in the Outbreak Verification List. Follow up was undertaken because initial reports
suggested international public health importance. Of the 69 events, 58 (84%) were excluded from the Outbreak
Verification List because they did not meet the criteria for outbreaks or for international public health importance.
Four (6%) reports were unsubstantiated, including two reports of smallpox, one of yellow fever, and one of viral
hemorrhagic fever. In seven (10%) events, follow up could not be completed, and the verification process remained
inconclusive. The 69 excluded events did not differ from the 246 disseminated outbreaks with regard to their
distribution by WHO region, initial source of information, or type of disease or syndrome. A reassessment of the 62
verified events did not identify any outbreaks that should have been classified retrospectively as of international
Whenever the outbreak verification team invokes a verification process, assistance to the country in which
the event takes place is offered directly by WHO headquarters or through the WHO regional and country offices.
Past examples of such assistance include supply of essential materials to outbreak sites, transport of laboratory
specimens from the field to appropriate diagnostic facilities, organization of vaccination programs, training of field
staff as part of outbreak control measures, or deployment of field teams for disease control. Recent examples of
direct assistance by WHO and its partners in field investigations include support for Rift Valley fever in Kenya and
Somalia, monkeypox in the Democratic Republic of the Congo, avian influenza (H5N1) in Hong Kong,
Special Administrative Region of China, Ebola hemorrhagic fever in Gabon, relapsing fever and acute
respiratory infections in southern Sudan, influenza in Afghanistan, and Marburg virus infection in the Democratic
Republic of the Congo.
Outbreak verification is a new approach to global disease surveillance. Its aim is to improve epidemic
disease control by providing accurate and timely information about important disease outbreaks. While the
outbreak verification concept has remained unchanged since its start in early 1997, its daily application continues
to evolve as more data are gathered and more experience is gained.
Currently, most outbreak reports are received from the media, and field personnel are mainly contacted for
assistance with verifying reported events. This approach is subject to information bias, which results from the
uneven dispersal and use of modern technology throughout the world. Also, different languages are not equally
represented in the news media or addressed by electronic search engines. While these shortcomings are partly offset
by the information received directly from the WHO network, a more active dialogue should be established with
field personnel. Receiving primary information directly from the field will lead to earlier detection of important
events and events that escape identification. Although thought to be small, the number of important outbreaks
recognized only locally is unknown.
The number of outbreak reports selected for verification is small compared with the number of reports
received by the outbreak verification team. While the criteria for selecting outbreak reports for verification have
been established, their application requires an individual assessment of each single event. Some see in this
selection process a lack of transparency and argue that the reader is the best judge of what to believe. This may be
the case for those who have time, good information networks, and access to advanced communication technology.
However, most international public health workers have none of these and are poorly informed about such events.
WHO therefore considers that sharing filtered information is valuable. In a recent survey among the Outbreak
Verification List recipients, 72% percent of the respondents stated that the list was very useful or indispensable to
their work, and 70% cited the list as their first source of information about a particular event.
Applying the selection criteria is also difficult if available information is insufficient to determine if an
event should be classified as an outbreak (number of cases in excess of expected numbers). This problem arises
particularly when dealing with endemic diseases in the absence of established epidemic thresholds. The Outbreak
Verification List addresses the issue by mentioning events with clear implications for international public health
that are not regarded as outbreaks in a separate Notes section. The Outbreak Verification List shares relevant and
often sensitive information with public health professionals while the verification process is still under way.
Although this has led on rare occasions (<1%) to the dissemination of information about unsubstantiated events,
the Outbreak Verification List usually provides timely and accurate information about important disease outbreaks.
Because of its confidential nature, the Outbreak Verification List is not in the public domain, and some
argue that WHO is not timely in addressing the information needs of the public about epidemics. However,
WHO communicates information as soon as it is verified. In some instances, this takes time, but the delay prevents
release of inaccurate information.
Industrialized countries feature infrequently in the Outbreak Verification List because it is assumed that
they can deal with outbreak situations. This is, of course, not always true and leads to an overrepresentation of
developing countries in the Outbreak Verification List. However, most outbreaks in developing countries are
contributed by nations with complex emergencies. While the reporting may accurately reflect the breakdown of the
public health and social infrastructures, it may also contain an element of overreporting due to heightened media
attention associated with complex emergencies.
As a new concept, early outbreak verification efforts focused mainly on the development of process
indicators (information gathering, verification, information dissemination). More outcome-oriented indicators need
to be addressed to assess the outbreak verification impact at country level and within WHO. While providing public
health professionals with timely and accurate information about important disease outbreaks improves epidemic
preparedness and response, this has not been quantified. Possible outcome indicators could include the time
interval between first report and the commencement of investigation and control efforts or the proportion of
outbreaks with laboratory confirmation. Additional tasks to be addressed in the future are more detailed analyses,
including electronic and print mapping to provide both baseline (endemic) and outbreak information, and
standardized reports to regions and countries.
This article was written by Dr. Grein, a medical officer in the Department of Communicable Disease Surveillance and Response at the World
Health Organization in Geneva, Switzerland. His activities at WHO include the investigation and control of epidemics and training in field epidemiology. The entire article, references and other pertinent information can be found at www.cdc.gov/ncidod/eid/vol6no2/grein.htm