Evaluation of clinical case definitions of influenza: Detailed investigation of patients during the 1995-1996 epidemic in France

Using clinical predictors, we evaluated clinical case definitions of influe nza during the 1995-1996 outbreak in France. Thirty-five general practition ers collected virological specimens and clinical data. Predictors of influe nza virus infection were selected with logistic regression models. The resu lts varied with the influenza virus subtype: temperature of >38.2 degrees C , stiffness or myalgia, rhinorrhea, and cough were predictive of influenza A/H3N2, whereas fatigue, lacrimation or conjunctival injection, and the abs ence of stiffness or myalgia were predictive of influenza A/H1N1. On the ba sis of this analysis and data from the literature, 12 clinical case definit ions were evaluated for their abilities to diagnose influenza virus infecti on. They were associated with positive predictive values of 27% to 40% and negative predictive values of 80% to 91%. We conclude that focused studies evaluating clinical case definitions of influenza with use of subsets of pa tients should accompany population-based disease surveillance for optimal e stimates of the disease burden associated with influenza epidemics.