<P> Public health surveillance (also epidemiological surveillance, clinical surveillance or syndromic surveillance) is, according to the World Health Organization (WHO), "the continuous, systematic collection, analysis and interpretation of health - related data needed for the planning, implementation, and evaluation of public health practice ." Public health surveillance may be used to "serve as an early warning system for impending public health emergencies; document the impact of an intervention, or track progress towards specified goals; and monitor and clarify the epidemiology of health problems, to allow priorities to be set and to inform public health policy and strategies ." </P> <P> Public Health surveillance systems can be passive or active . A passive surveillance system consists of the regular, ongoing reporting of diseases and conditions by all health facilities in a given territory . An active surveillance system is one where health facilities are visited and health care providers and medical records are reviewed in order to identify a specific disease or condition . Passive surveillance systems are less time consuming and less expensive to run but risk under - reporting of some diseases . Active surveillance systems are most appropriate for epidemics or where a disease has been targeted for elimination . </P>

What is the purpose of surveillance in epidemiology
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