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Home Eurosurveillance Weekly Release  2006: Volume 11/ Issue 51 Article 3
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Eurosurveillance, Volume 11, Issue 51, 21 December 2006

Citation style for this article: Kaiser R, Coulombier D. Epidemic intelligence during mass gatherings. Euro Surveill. 2006;11(51):pii=3100. Available online:

Epidemic intelligence during mass gatherings

R Kaiser, D Coulombier (

European Centre for Disease Prevention and Control, Stockholm, Sweden

Public health is an important aspect of the planning for mass gatherings which include major sport events (e.g. the Olympic Games, the FIFA World Cup), other spectator events (e.g. air shows, concerts), and political or business (e.g. conferences, trade fairs) or religious events (e.g. the Hajj). The sizes of mass gatherings vary: for example, there were around 3.2 million spectators during the FIFA World Cup in Germany in 2006, compared with 5000 demonstrators who set up a camp close to the 2005 G8 Summit in Gleneagles in Scotland [1,2].

The particularly high population density at a mass gathering event may facilitate transmission of infectious diseases, or attract deliberate releases of chemical, biological or radioactive agents, or bomb attacks [3,4]. Visitors may come to the gathering with infections (such as undetected tuberculosis) or may be susceptible to pathogens circulating at the location of the event (for example, unvaccinated people who travel to a country where there is a measles outbreak). An example of an acute outbreak at a mass gathering is the norovirus outbreak at an international scout summer camp in the Netherlands in 2004 [5].

Furthermore, gatherings with international participants potentially pose specific challenges for implementing control measures, such as contact tracing in case of an outbreak. Finally, when events attract a high level of media attention, health authorities need to be prepared to issue timely communications to the responsible institutions and, possibly, the general public, in case of a potential or actual public health threat (not only outbreaks).

As part of the medical service preparations for a mass gathering event, health authorities frequently enhance their surveillance systems to enable earlier warning of potential public health threats. ‘Epidemic intelligence’ can be defined as all the activities related to early identification of potential health threats, their verification, assessment and investigation, carried out in order to recommend public health measures to control them [6]. In order to detect all potential threats, epidemic intelligence should also include non-communicable health hazards.

When is epidemic intelligence needed? The difficulties of defining mass gatherings

The following challenges exist when determining which mass gathering events require epidemic intelligence gathering:

  • It is difficult to define what a mass gathering is, and to categorise different types in relation to their potential risks to public health. As far as epidemic intelligence and public health are concerned, mass gatherings need to be differentiated from humanitarian emergencies. Mass gatherings are non-emergency events where there is generally time for appropriate planning, while humanitarian emergencies require different resources and approaches.
  • There can be similar visitor numbers and health risks at organised mass gatherings that attract media attention (such as the Olympics) and those that do not, such as trade fairs, international airports or mass tourism settings where large numbers of people gather every day. However, there is low awareness of the potential need for epidemic intelligence during the non-organised gatherings.

The lack of a definition of mass gatherings, and low awareness within organising committees, may be the main reasons why public health preparedness has not been a major priority for such events. However, there are indications that this may have changed after the terrorist attacks in New York on 11 September 2001 and the emergence of SARS and avian influenza. Public health authorities have been involved in planning for the major sports events in Europe in 2006, the Torino Winter Olympics [7] and the FIFA World Cup in Germany [1].

The following points should be considered for prioritising the need for epidemic intelligence and public health planning before a mass gathering event.

  • number of people expected to gather;
  • kinds of people gathering for the event (ages, nationalities and other characteristics; for example, summer camps will attract adolescents and young adults from the country where the event is held, while an international event like the Hajj attracts people from all over the globe and a wide range of socioeconomic classes);
  • duration of the event;
  • expected public attention or political importance (the event may attract deliberate releases and constitute a reason to invest in preparedness);
  • potential spread of infection or other effects to other sites in the community.

Planning epidemic intelligence during mass gathering events
The planning process for epidemic intelligence during mass gatherings should include the following steps:

  • Gathering of experience from previous events, thorough review of the literature, participation in the planning of events, or consultations;
  • Assessing potential public health risks during the mass gathering and the capacity of the existing surveillance and response structures to detect and control them. The risk assessment should take into account the accessibility of the event site, the type of venue (e.g. outdoors or indoors, stadium or larger, less well-defined space), the likely demographics, risk factors and susceptibility of the people attending, environmental factors (such as weather conditions, food handling, water quality and sewage disposal), and communicable and non-infectious hazards of concern;
  • Defining the epidemic intelligence objective during the mass gathering. An example for the general objective for epidemic intelligence during a mass gathering is to quickly detect emerging disease outbreaks or unusual patterns of disease or injury that might require rapid intervention immediately before, during or after the event[8];
  • Developing an epidemic intelligence strategy, including a budget and human resources plan, and establishing a network with national and international stakeholders if necessary;
  • Developing reporting and analysis systems with backup mechanism in case of network failure;
  • Testing epidemic intelligence during smaller events and/or exercises.

Surveillance methods during mass gatherings

The routine collection of surveillance data can be enhanced and the scope of surveillance widened in different ways, according to the nature of the event:

1. Enhancing existing surveillance systems
Enhancing existing surveillance systems usually consists of improving the completeness of case reporting by requesting that the sources of information (e.g. clinics) provide more timely and complete reporting and adjusting the flow of data to ensure timely notification to enable health authorities to trigger appropriate control measures if necessary. Systems relying on a sample of sources (sentinel), such as the one for influenza-like illnesses, can be used for additional conditions (e.g. diarrhoeal diseases). Enhancement activities are usually limited to cities or the administrative areas involved in the mass gathering.

2. Developing an additional community-based system
Additional temporary community-based surveillance may use syndromic case definitions for conditions presenting a potential risk, e.g. for diarrhoeal diseases or lower respiratory syndromes. Syndromic surveillance involves the collection and analysis of data on clinical case features, such as signs and symptoms that are present (and available for analysis) before a definitive diagnosis [9]. Syndromic surveillance systems, although less specific, have the advantage of more rapid reporting, especially if information is actively obtained, which is directly entered into an electronic system, and automatically categorised. Such systems have been implemented in emergency medical departments [7,10] and sometimes general practices when the information systems allowed it. The added value of such systems has not been shown and should be studied. While more traditional existing surveillance systems are well connected to response systems, additional syndromic systems may cause problems if actions resulting from a generated signal are not clearly defined and assigned in advance.

3. Setting-up venue/event-specific surveillance systems
Some mass gatherings have clinics onsite at venues or specific locations (e.g. an Olympic village or media centre). Managing these facilities is usually the responsibility of the organising committee. There should be daily reporting to public health authorities of activity (number of consultations) classified according to a predefined short list of syndromes.

Additional approaches may include collection of unusual types of surveillance data [11], e.g. sales of over-the-counter drugs, increase in health-related web queries, or number of orders for blood cultures, stool cultures, or chest x rays.

Detection algorithms and thresholds
Systems can be set up to automatically detect abnormalities in the surveillance data [11]. Automated tests should be complemented by human visual assessment of changes over time (‘eyeballing’). An alarm may be triggered if an observed case count exceeds the 90% or 95% confidence interval of the predicted count. Historical baseline data are usually not available for mass gatherings. Therefore, departure from the expected may rely on detection of short term changes, such as comparing cases observed on a given day to the average of previous seven days, using a Poisson test, or the percentage of visits for one syndrome compared to the average of visits during the previous seven days, using a binomial test.

Planning should take into consideration the potential nature of any alerts and the type of transmissions, sensitivity and specificity of the analysis algorithms, control for seasonal and daily trends (e.g. higher case numbers in emergency departments during the weekend), availability of historical data as a baseline, and resulting denominator issues due to the temporary population changes during the event. Existing statistical resources and available software may also be useful.

Dissemination of information
The potential need to prepare a daily report on the epidemiological situation for decision makers and the public has considerable implications for planning of the epidemic intelligence process during the mass gathering event. Some public health planners during previous mass gatherings limited access to reports to partner organisations only, whereas others made the reports (sometimes including the underlying data) generally available (e.g. on the event’s website) [12]. During a crisis, a high level of transparency, including daily reporting, may contribute to general awareness raising and building of trust between the responsible authorities and the public.

Future developments
In 2006, the European Centre for Disease Prevention and Control (ECDC) worked in close collaboration with national health authorities during the Winter Olympics in Torino and the FIFA World Cup in Germany, providing event-based surveillance and back up support in case of a crisis. The ECDC will continue to collaborate with European national health authorities and international partners on public health preparedness during mass gatherings.
Monitoring and evaluation are needed to increase knowledge of the potential benefits of different models of epidemic intelligence and their cost-effectiveness during mass gatherings.

This article is based on discussions during a recent epidemic intelligence consultation organized and held by the European Centre for Prevention and Disease Control (ECDC) on 6-8 November 2006 in Stockholm and brought together national epidemic intelligence and surveillance experts from EU countries plus Iceland, Norway, and Switzerland, as well as representatives from the European Commission, World Health Organisation, Health Canada and the Caribbean Epidemiology Centre.

  1. Josephsen J, Schenkel K, Benzler J, Krause G, Preparations for infectious disease surveillance during the football World Cup tournament, Germany 2006. Euro Surveill 2006;11(4):E060427.2. Available from:
  2. The Health of the Population of Forth Valley 2005-2006. Available from:
  3. Editorial team. Hajj 2007: vaccination requirements and travel advice issued. Euro Surveill 2006;11(11):E061130.1. Available from:
  4. Meehan P, Toomey KE, Drinnon J, Cunningham S, Anderson N, Baker E. Public Health Response for the 1996 Olympic Games JAMA. 1998;279:1469-1473.
  5. Norovirus outbreak at an international scout jamboree in the Netherlands, July-August 2004: international alert. Eurosurveillance Weekly [1812-075X]. 2004 Aug 12;8(33) 040812. Available from:
  6. Kaiser R, Coulombier D, Baldari M, Morgan D, Paquet C. What is epidemic intelligence, and how is it being improved in Europe?. Euro Surveill 2006;11(2):E060202.4. Available from:
  7. Epidemiological Consultation Team. Surveillance system in place for the 2006 Winter Olympic Games, Torino, Italy, 2006. Euro Surveill 2006;11(2):E060209.4. Available from:
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  10. Hadjichristodoulou C, Mouchtouri V, Soteriades ES, Vaitsi V, Kolonia V, Vasilogiannacopoulos AP, Kremastinou J. Mass gathering preparedness: the experience of the Athens 2004 Olympic and Para-Olympic Games. J Environ Health. 2005 May;67(9):52-7.
  11. Gesteland PH, Gardner RM, Tsui FC, Espino JU, Rolfs RT, James BC, Chapman WW, Moore AW, Wagner MM. Automated syndromic surveillance for the 2002 Winter Olympics. J Am Med Inform Assoc. 2003 Nov-Dec;10(6):547-54
  12. Coulombier D. Surveillance for the World Cup, France, 1998 . Eurosurveillance Weekly [1812-075X]. 1998 Jun 11;6(24) 980611. Available from:

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