Rationale, aims and objectives Viral infections are characteristic of spread rapidly, high incidence, high mortality and difficult diagnosis, treatment and prevention contrast with other types of infectious diseases.Acute fever is the most common clinical symptom for viral infectious diseases.It is necessary to identify risk factors for viral infectious patients with acute fever and formulate an activation criteria of early warning viral infeetiosity score (EWVIS) system to alert out-patient clinic doctors.Methods Logistic regression analysis was used to determine risk factors for viral infectious diseases from the clinical data of 563 patients with acute fever.Risk factors were weighted and an EWVIS was formulated.A ROC analysis of weighted cumulative score was performed to evaluate the diagnostic accuracy of EWVIS, and the Kappa test used to confirm diagnostic reliability.A x2 test for trend was applied to determine the relevance between EWVIS and the incidence of viral infections.Results Risk factors for viral infections included conjunctival hyperemia, rash, diarrhea, increased alanine aminotransferase (ALT), and abnormal percentage of peripheral neutrophils (NE%).Risk factors were weighted and tabulated.The areas under the ROC curves of the EWVIS was 0.970 and >4 points predicted viral infectious diseases, the Kappa values was 0.835.As the score increased, the incidence of viral infections increased.The EWVIS was specific for viral infections relative to bacterial infections.Conclusions Risk factors for viral infections have been identified, quantified and formulated into a table of EWVIS that have high diagnostic accuracy and reliability for the early identification of viral contagious diseases.Funding National Key Technology R&D Program during the Eleventh Five-year Plan Period [2007BAI24B06].