Perspectives on epidemiologic surveillance in the 21st century.

This paper describes the importance of epidemiologic surveillance as a systematic, ongoing and population-based system for early warning and program development in the 21st century. Such a system routinely collects data on three classes of indicators (health outcomes, risk factors and intervention strategies) to set up both an early warning system (to identify associations and make predictions on health outcomes) and a program development system (to assess the need for intervention strategies, to plan and implement such strategies and to assess their effectiveness). A comprehensive surveillance system must be systematic (evidence-based selection of indicators, not hypothesis-driven), ongoing (continuous data collection, including repeated surveys) and population-based (whole population, or representative samples of the population). Such a system need not be developed from scratch, but can be based on linkage of existing databases and collection of additional information for identified data gaps. The initial steps for selecting indicators and creating a prototype framework for a comprehensive surveillance system are proposed to stimulate further discussion. It is suggested that surveillance systems should be more widely used in public health.