Published on 08/06/2011

Missions and fields 

Global health surveillance

In a globalized environment where the flow of goods and people is constantly on the rise the risk of epidemics also becomes globalized. In order to fulfil its public health mission, InVS must not only monitor health at all times on the national territory, but also identify and characterize any health risks as quickly as possible as they arise in foreign countries and which are likely to affect the French people. The SARS epidemic of 2003 illustrated the what the nature and scale of these new threats might look like.

Over the past few years we have witnessed the development of many supranational and global networks that collect, analyze and circulate information pertaining to health surveillance and alerts. Although very useful the information collected and circulated by these international bodies (WHO, ECDC, etc.) only partly covers France's requirements, among other reasons because France's départements and overseas territories are located on three different continents.

Since December 2002 InVS has developed a global surveillance mechanism.

Objectives and principles

The purpose of global surveillance is to identify any threats arising in foreign countries that are likely to impact the health of the population living in France or the French people living abroad, as well as to warn people and to issue any information deemed relevant.

This is based on interpreting and appropriately identifying unusual events that are likely to spread and which appear as serious. The nature of such events is not predetermined; the nature of unstructured data is very diverse and stems from multiple and non-predetermined sources. This can include unverified rumours coming from the media, reliable information from competent and authoritative sources or data stemming from classic surveillance and alert systems.

Global surveillance is not restricted to identifying unusual or serious events. It is also used to describe epidemiological features (attack rates by age and gender, risk factors, spreading of the disease in both space and time, etc.) based on the information available (in all accessible sources, both informal and formal). Such features are particularly important for unknown or poorly understood health events (such as emerging infectious agents or exposure to an agent whose potential impact is poorly understood).

Global health surveillance complements the epidemiological surveillance of the French people as well as all other mechanisms.

Global surveillance is different from global monitoring: in other terms, it is based on existing available data and its purpose is not to be comprehensive.

Global surveillance process at InVS

A great deal of information is collected and its reliability is often questionable. Strict methodology is paramount in order to obtain the most reliable and relevant information possible. The methodology used involves identifying any signals that could reveal a health threat; those signals are sorted, verified and validated, then all available data is analyzed and interpreted, and lastly the information and analyses are communicated where necessary.

Identifying signals

There are two types of signals:

  • Primary signals: unprocessed signals stemming from a large variety of sources and most often limited to the description of events (little or no scientific information);
  • Secondary signals (signals that have already been processed or alerts that have already been characterized) coming from other countries or institutions.

Primary signals stem from two major types of sources:

  • Informal sources are mostly where primary alert signals come from. These are chiefly represented by the media as well as exchange and information networks that can be accessed through the Internet (forums, etc.). They provide an alternative source of information to official sources. Such information is generally easy to access but there are two major limitations: the information is often unreliable and there is a significant amount of such information;
  • Official sources that help to identify global health threats are relatively few in number. Official sources basically include governments (Ministry of Health, Ministry of Agriculture, public health institutes, laboratories, etc.), the WHO for human health, the OIE for animal health and zoonoses, regional institutions such as the ECDC, regional networks such as the EpiSouth network for the Mediterranean area, disease-specific monitoring networks, NGOs, etc.

Signals are identified using specialized tools that automatically collect any information which may be related to health alerts; information is collected from the Internet using keywords or sequences of keywords.

Sorting signals

As there is a great deal of raw signals or signals that have already been processed it is important to define criteria that will help to identify events that need to be analyzed and monitored. These criteria help to answer two questions:

  • Is the threat serious?
  • Is the health threat likely to affect the national territory or any French people in a foreign country (expatriates, tourists, etc.)?

Three types of criteria are jointly used: geographic and population, criteria related to the seriousness of the threat, and criteria related to the features of the agent in question.


Signal sorting criteria


Seriousness / Dynamic


- Risk of reaching the national territory (including overseas territories)
- Risk of importing the disease on the national territory (including overseas territories)
- Reaching an area close to France (including overseas territories)
- Reaching one of the main home countries of migrants in France
- Reaching a country where there is a strong French expatriate community
- Reaching a destination popular with French tourists and travellers
- Large gatherings, pilgrimages, etc.

- Lethality
- Number of deaths
- Mortality
- Morbidity
- Incidence
- Seriousness, incidence of hospitalizations
- Sequelae 
- Time frame (duration, dynamics of the epidemic)
- Locations: rural-urban; isolation from affected area; population density, etc.
- Groups at risk
- Specific populations (health-care personnel, hospitals, etc.)

- Virulence
- Pathogenicity 
- Communicability
- Mode of transmission
- Ability to spread
- Existence of prevention and control resources, resources that are available and easy to implement
- Epidemiological and biological changes (resistance, geographical distribution, etc.)
- Level of knowledge about the agent

Any emergence of a new agent is analyzed as being a potentially hazardous emergence


Media events that need to be put in their epidemiological context



Validation and verification

As information coming from informal sources cannot be considered reliable it must be checked. Only those signals that meet the selection criteria will be validated, and only those signals that have been validated may be communicated to the public. This is the most complicated step of the process, but it is an essential one. The idea is to check and supplement information available from reliable sources such as Institutes, Health Ministries, laboratories of relevant countries, the WHO, regional networks, NGOs, embassies, etc. The press is not considered a validated source of information.


Analysis is expected to characterize the signal, describe the alert and assess the level of the alert. It relies on a description of the event, knowledge of the danger as well as risk quantification and control measures. This is one of the main added values of global surveillance.


Depending on the target audience and the nature of health signals, global surveillance has a variety of support elements:

  • Institutional targets (Health Ministries, Ministries of Foreign Affairs, etc.): within the French Institute for Public Health Surveillance there are specific mechanisms to inform or alert relevant institutional partners as quickly as possible, and in particular the Ministry of Health. Information must be delivered so as to inform the decision-making process;
  • Public health network and partners: the weekly international bulletin and its theme-based or special editions are intended for InVS partners as part of the national and international public health network, and also for health-care professionals (hospital physicians and health-care for travellers) and can be accessed through the InVS website.

The Weekly International Bulletin (BHI) presents a weekly review of health crises pertaining to new health events that occurred in foreign countries and which are likely to constitute a health threat on the national territory and for French people abroad. The BHI does not provide a comprehensive account of all international health alerts or a weekly follow-up of health crises (except in special situations such as the avian flu). Depending on the nature of the event updates might be included in the bulletin if they show a change in the health crisis epidemiology (a significant increase in the number of cases, geographical expansion, nature of groups at risk, etc.).

Theme-based and special editions: theme-based editions provide further understanding on complex issues as well as updated knowledge on the topic in question, while special editions help to communicate urgent information outside the BHI’s normal publication periods.


Surveillance is in line with InVS’s international mission. Ever since it was implemented it has helped to inform health-care authorities on risks related to previously unknown medical conditions on the national territory (such as SARS in 2003, the A/H5N1 avian flu in 2004, the chikungunya virus in 2005, the A/H1N1 flu in 2009) even before the first cases were imported or identified. Most alerts involve infectious cases but non-infectious events, such as contaminated products, are also covered. In addition to alerts global surveillance also helps to describe health-care crises (number of cases, number of deaths and hospitalizations for severe forms, age of cases, geographical distribution, etc.) as well as changes in terms of the spreading of the disease. In cases of unknown medical conditions it is often the analysis of features of cases described at international level that helps to develop definitions of cases used in France and thus monitor these emerging diseases. Communication aids developed as part of global surveillance make it possible to provide information presented in summary format that has been verified, analyzed and placed in its epidemiological context. This also helps to not only let hospital physicians know that cases rarely diagnosed could potentially be imported in France, but also to inform practitioners in providing advice to travellers.


Systems depend on access to information, which varies greatly from one country to another. The ever-increasing number of signals circulating on the Internet greatly complicates the identification of relevant information and is the cause of many “media alerts” that overburden facilities involved in global surveillance, while human and technical resources remain constant.

Prospects of global surveillance

InVS continues to work with organizations such as the ECDC, WHO and others in the area of global surveillance, and is also developing new partnerships in the Mediterranean basin through the EpiSouth network set up in 2006.

Surveillance tools are being revamped on a regular basis in order to adapt to an ever-changing environment. Although the purpose of health-care surveillance is to monitor health-related crises, the communication tools available are not always suited to such uses. In the medium term, tools currently in development should make it easier to look up information in available documents. InVS is involved in an international project called EAR (Early Alerting and Reporting), one of the objectives of which is to develop a common tool for global surveillance (link to EAR-GHSAG).

Global surveillance is also involved in the “travellers’ health” topic (which is part of the monitoring of imported diseases).


Priority geographical areas for global surveillance


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