Development and validation of the Influenza Intensity and Impact Questionnaire (FluiiQ™)

Clinical trials of new agents to reduce the severity and impact of influenza require accurate assessment of the effect of influenza infection. Because there are limited high-quality adult influenza Patient Reported Outcomes (PRO) measures, the aim was to develop and validate a simple but comprehensive questionnaire for epidemiological research and clinical trials.

Construct and item generation was guided by the literature, concept mapping, focus groups, and interviews with individuals with laboratory-confirmed influenza and expert physicians. Items were administered to 311 people with influenza-like illness (ILI) across 25 US sites. Analyses included classic psychometrics, structural equation modeling (SEM), and Rasch analyses.

Concept mapping generated 149 concepts covering the influenza experience and clustered into symptoms and impact on daily activities, emotions, and others. Items were drafted using simplicity and brevity criteria. Eleven symptoms from the literature underwent review by physicians and patients, and two were removed and one added. The symptoms domain factored into systemic and respiratory symptoms, whereas the impact domains were unidimensional. All domains displayed good internal consistency (Cronbach α ≥ 0.8) except the three-item respiratory domain (α = 0.48). A five-factor SEM indicated excellent fit where systemic, respiratory, and daily activities domains differentiated patients with ILI or confirmed influenza. All scales were responsive over time.

Patient and clinician consultations resulted in an influenza PRO measure with high validity and good overall evidence of reliability and responsiveness. The Influenza Intensity and Impact Questionnaire (FluiiQ™) will improve the evaluation of existing and future agents designed to prevent or control influenza infection by increasing the breadth and depth of measurement in this field.