Good surveillance has been identified as the first major goal in preventing EIDs that arise naturally or through terrorist activities [10-12]. Preventing or restricting the impact of an EID is dependent on the ability to rapidly detect the first cases [13]. The earlier cases are identified, the more likely it is that an intervention will prevent further cases, especially if the intervention occurs in advance of the logarithmic growth phase of the epidemic.
The US Centers for Disease Control and Prevention (CDC) define surveillance systems as those that collect and analyze morbidity, mortality, and other relevant data and facilitate the timely dissemination of results to appropriate decision makers [14]. Such systems, therefore, consist of routine data collection, data analyses, followed by a response when required. It is this element of decision and timely response based on interpretation of the data that makes surveillance different from monitoring, making it more than just a system for event detection. Surveillance is ‘action-oriented’, wherein ‘real-time’ decisions are linked to current findings. Therefore, surveillance includes timely response to the data. Monitoring, on the other hand, does not necessarily include a timely response. Monitoring sacrifices timeliness for accuracy, looking to make summary reports of what has happened rather than what is happening (see Figure 1). A disease surveillance system specifically designed for EIDs is sometimes referred to as an early warning system, and therefore these two terms are used interchangeably in this paper.