Content validity and psychometric properties of the inFLUenza Patient-Reported Outcome Plus (FLU-PRO Plus(©)) instrument in patients with COVID-19

PURPOSE: A well-defined and reliable patient-reported outcome instrument for COVID-19 is important for assessing symptom severity and supporting research studies. The InFLUenza Patient-Reported Outcome (FLU-PRO) instrument has been expanded to include loss of taste and smell in the FLU-PRO Plus, to comprehensively cover COVID-19 symptoms. Our studies were designed to evaluate and validate the FLU-PRO Plus among patients with COVID-19. METHODS: Two studies were conducted: (1) a qualitative, non-interventional, cross-sectional study of patients with COVID-19 involving hybrid concept elicitation and cognitive debriefing interviews; (2) a psychometric evaluation of the measurement properties of FLU-PRO Plus, using data from COMET-ICE (COVID-19 Monoclonal antibody Efficacy Trial—Intent to Care Early). RESULTS: In the qualitative interviews (n = 30), all 34 items of the FLU-PRO Plus were considered relevant to COVID-19, and participants determined the questionnaire was easily understood, well written, and comprehensive. In the psychometric evaluation (n = 845), the internal consistency reliability of FLU-PRO Plus total score was 0.94, ranging from 0.71 to 0.90 for domain scores. Reproducibility (Day 20–21) was 0.83 for total score, with domain scores of 0.67–0.89. Confirmatory factor analysis with the novel smell/taste domain demonstrated an acceptable fit to the data. CONCLUSION: The content, reliability, validity, and responsiveness of the FLU-PRO Plus in the COVID-19 population were supported. Our results suggest that FLU-PRO Plus is a content- and psychometrically-valid, fit-for-purpose measure which is easily understood by patients. FLU-PRO Plus is a suitable PRO measure for evaluating symptoms of COVID-19 and treatment benefit directly from the patient perspective. Trial Registration: ClinicalTrials.Gov: NCT04545060, September 10, 2020; retrospectively registered. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s11136-022-03336-3.