Introduction

This chapter provides an overview of the basic theory of early warning for infectious diseases, including definitions of surveillance, early warning and prediction; the characteristics of early warning (surveillance, information for action, timeliness, insufficiency, and the uncertainty of information); a conceptual framework of an early warning system for infectious diseases (the target setting, data collection and analysis, disseminating early warning signals, response actions, and evaluation); classifying early warning based on the data sources (case-based, event-based, laboratory-based, or syndromic surveillance). The significance of early warning for infectious diseases, the status quo and research and application trends in the field are also highlighted.