I. Introduction
Before the occurrence of an event and when the evidence of causality and reaction relationship has not been determined, the area, scale, nature, influencing factors, radiation range, harm degree, and possible consequences of the event can be comprehensively evaluated based on the collected information and intelligence data. Appropriate means must be adopted to issue warnings of event threats in advance, and corresponding actions must be taken to prevent the occurrence and development of events to the maximum extent [1]. Early warning of public health emergency refers to the warning signal issued before or in the early stage of a public health event to remind of the possibility of an outbreak or epidemic of a public health event or the risk that the scope of its occurrence may expand [2].