In the last decades, the world has undergone rapid changes including demographic explosions and massive urbanization, population movement, increase in international trade and travel, emergence of new pathogens, use of techniques which induce new risks, chemical and nuclear accidents, environmental disasters and introduction of the threat of criminal acts and bioterrorism.
To respond to this changing environment, the International Health Regulations (IHR) were revised in 2005. The IHR expands usual infectious disease notification to include surveillance of public health events from various origins (e.g. nuclear, chemical or unknown), and prompts Member States to develop the capacities of their surveillance systems to detect, assess, notify and respond to all acute health events or health risks that may constitute a threat to human health. As the Regulations note, “To comprehensively meet the early warning and alert requirements of the IHR, there is a need to strengthen and develop both routine, or indicator-based, surveillance and event-based surveillance”.
Conventional surveillance is based on restrictive lists of predominantly infectious diseases. Many countries have already implemented the change to a comprehensive “all hazards” surveillance.
However, this approach represents a major paradigm shift that may require significant restructuring of the public health surveillance system. Public health surveillance serves two main objectives:
To measure disease burden, including monitoring morbidity/mortality trends, in order to effectively guide control programmes and the corresponding allocation of resources; and
To early detect public health events requiring rapid investigation and response, in order to ensure that events of all origins are rapidly detected and controlled. The organized mechanism to reach this objective is referred to as Early Warning and Response (EWAR).
The efficient collection of pertinent information informs and guides the public health response to all acute public health events including: unknown, unusual or unexpected diseases or disease patterns of all origins (i.e. biological, chemical, radiological or nuclear) as well as hazards that could potentially pose a risk to human health such as heat waves, natural disasters or contaminated food items.
Sources of information that can be used for the early warning function go far beyond traditional disease-based surveillance (including laboratory confirmation) and syndromic surveillance. They encompass environmental/ecological surveillance (e.g. vector density, water/air quality, climatic data, etc.) and health-related behavioural information (e.g. monitoring of absenteeism in schools or in workplaces, medicine sales and paramedical product such as insect repellent, activities on internet or social networks, etc.) (Figure 1). EWAR should therefore be designed to be sensitive and to detect and respond rapidly to signals and alerts coming from both formal and informal sources, within and outside of the health sector.