Review of the 2003 National Syndromic Surveillance Conference--lessons learned and questions to be answered.

Syndromic surveillance is a rapidly evolving field within public health practice. Substantial experience has been gained in learning how to conduct syndromic surveillance, informed by a growing body of research and practice, including refinement of surveillance methods, development of new tools for analysis and evaluation, findings from statistical models and applied evaluations, and expansion of syndromic surveillance to uses beyond preparedness for biologic terrorism. Despite these advances, additional evaluation is needed to help health departments determine whether to conduct syndromic surveillance. This paper summarizes the lessons learned from the 2003 National Conference on Syndromic Surveillance, which provided a foundation for defining a research and evaluation agenda and for developing preliminary guidance for public health agencies planning to implement syndromic surveillance.