Factors associated with intensity of symptoms in patients seeking medical advice for flu

The aim of our study was to explore factors associated with the intensity of signs and symptoms of flu-like illness, on adult patients seeking medical advice for flu. We analysed 554 index patients (56% influenza positive) included in a prospective household contact study during winter 1999-2000. The intensity of illness was calculated from 19 symptoms recorded by the GP during the visit (Z-score-GP) and from 13 symptoms reported by the patients at the first day of follow-up (Z-score-Pat). The two Z scores were highly correlated (intraclass correlation of 0.43). Multivariate regression identified the following predictors of Z-score-GP: influenza-positive diagnosis (+0.26, p = 0.002) and gender female (+ 0.19, p = 0.03). The predictors of Z-score-Pat were: influenza-positive diagnosis (+0.39, p = 0.001), current smoker (+0.20, p = 0.04), gender female (+0.20, p = 0.02) and influenza vaccination (-0.39, p = 0.003). In influenza-positive patients, influenza vaccine was highly linked with a decrease in intensity of symptoms (Z-score-GP: -0.38, p = 0.04; Z-score-Pat: -0.49, p = 0.009). This last result was not found in influenza-negative patients. The study identifies tobacco use and influenza-positive diagnosis as predictors of increased intensity of influenza-like illness. Interestingly,, influenza vaccine decreased the intensity of symptoms in influenza-positive, but not in influenza-negative patients. (C) 2004 Elsevier B.V. All rights reserved.