Evaluation of symptoms in respiratory syncytial virus infection in adults: psychometric evaluation of the Respiratory Infection Intensity and Impact Questionnaire™ symptom scores

Background The Respiratory Infection Intensity and Impact Questionnaire (RiiQ™) is a patient-reported outcome measure designed to assess symptoms and impacts of respiratory syncytial virus (RSV) infection. This study evaluated the construct validity, reliability, and responsiveness of the RiiQ™ Respiratory and Systemic Symptoms Scale scores. Methods Prospective data were analyzed from a total of 1795 participants, including from non-hospitalized patients with acute respiratory infection (ARI) and no coinfections enrolled in a Phase 2b RSV vaccine study (RSV-positive: n = 60; RSV-negative: n = 1615), and two observational studies of patients hospitalized with RSV (n = 20; n = 100). Descriptive statistics, confirmatory factor analysis (CFA), test–retest intraclass correlation coefficients (ICCs), construct validity correlations (between a clinician-assessed clinical questionnaire and the RiiQ™ symptoms scale), known-groups validity, and responsiveness (correlations of change scores) were evaluated. Results Mean patient age ranged from 66.5 to 71.5 years and the majority of patients were female. Initial assessments in the vaccine trial (ARI Day 1) were suggestive of less severe illness than in the observational studies with hospitalized patients. CFA loadings (> 0.40) supported summary scores. ICCs exceeding the recommended threshold of 0.70 supported test–retest reliability for Respiratory and Systemic Symptoms, except in the small observational study. At the scale level, correlations were moderate to strong (| r | ≥ 0.3) and positive between the Respiratory Symptoms Scale and the related clinical questionnaire scores, reflecting measurement of similar symptoms in support of convergent validity. Correlations with change in Patient Global Impression of Severity > 0.30 supported responsiveness. Conclusions Psychometric tests applied to the RiiQ™ Symptoms scales provide evidence of its reliability, construct validity, discriminating ability, and responsiveness for use in clinical studies to assess the onset and severity of RSV symptoms.