Syndromic surveillance: the case for skillful investment.

PUBLIC HEALTH SURVEILLANCE is the ongoing, systematic collection, analysis, interpretation, and dissemination of data regarding a health-related event that enables public health authorities to reduce morbidity and mortality.1 Surveillance serves many public health functions—for example, estimating the burden of a disease or injury, portraying the natural history of a condition, determining the distribution and spread of illness, generating hypotheses and stimulating research, supporting disease control interventions, evaluating prevention and control measures, and facilitating planning.2 One important public health function of surveillance that is particularly relevant to biodefense is outbreak detection—that is, the ability to detect an abnormal rise in the frequency of a disease. Infectious disease outbreaks typically have been recognized either through accumulation in public health departments of case reports of suspected or diagnosed cases of a reportable disease, or by alert health care professionals, laboratorians, or the public bringing cases and clusters of diseases to the attention of public health authorities. Syndromic surveillance (defined below) is an approach to public health surveillance that may extend current capabilities to detect outbreaks early in their course. The concept of syndromic surveillance has not been clarified precisely, however, and expectations of what such surveillance can accomplish vary widely. Evaluation of the effectiveness of syndromic surveillance as one component of a comprehensive strategy for outbreak detection is urgently needed so policy makers can determine if, when, and how this technique should be applied.