From evaluation to continuous quality assurance of surveillance systems.

Surveillance systems have been described as the nerve cells of public health with afferent arms receiving information, cell bodies analysing the information and efferent arms initiating appropriate action or further distribution of information [1]. Increasing numbers of scientific publications on the methodology and evaluation of surveillance systems seem to underline the importance of surveillance systems in public health. The most often cited references in these publications appear to be the definition of public health surveillance by Thacker and Berkelman [2] and variations thereof, and the recommendations for evaluating surveillance systems from 1988 [3] and its update from 2002 written by working groups at the Centers for Disease Control and Prevention (CDC) in the United States[4].