The CDC defines surveillance as "the ongoing, systemic collection, analysis, interpretation, and dissemination of data about a health-related event for use in public health action to reduce morbidity and mortality and to improve health".
Traditionally, the primary method for collecting surveillance data was manual reporting of suspicious and notifiable clinical and laboratory data from clinicians, hospitals, and laboratories to public health officials. These systems provide information that can be utilized to estimate the magnitude of a public health problem, detect outbreaks, and determine the distribution of illness. This information is used to evaluate public health practice, stimulate research, and facilitate planning. However, these passive systems that rely on disease recognition and manual reporting are inadequate for rapidly identifying emerging patterns of illnesses.
Unlike traditional systems, syndromic surveillance is a system of data collection and analysis in which a clinical syndrome (signs and symptoms) or incident disease clusters are the focus of investigation rather than a specific disease. Systems are designed to collect data during the earliest manifestations of a disease, before a diagnosis is made. By identifying abnormally high visit rates for a specific syndrome, an early signal of BT attack may be detected. For example, in an anthrax attack the initial clinical presentation of patients with respiratory complaints would proceed a laboratory diagnosis by a few days. Early identification would allow public health officials to limit the scope of the outbreak. Ideally, these systems would not only identify disease outbreaks early but would do so with 100% sensitivity and a high degree of specificity. Systems may be designed for one or more of the following purposes: (1) to identify early cases of disease caused by terrorism, (2) to find aberrant patterns of disease in the context of a widespread exposure, (3) to track proxy syndromes by geographic and temporal distribution to identify possible cases, and (4) to provide reassurance that terrorism has not been found.
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