Reliability and Validity of an Instrument of COVID-19 Patient-Reported Symptoms in Outpatients

IMPORTANCE: Patient-reported outcome instruments are key in assessing COVID-19–related symptoms and associated burden. However, a valid and reliable instrument to assess symptom severity and progression among outpatients with COVID-19 is not yet available. OBJECTIVES: To assess the extent to which the Symptoms Evolution of COVID-19 (SE-C19) instrument is valid, reliable, and able to detect symptom changes in outpatients with COVID-19, as well as to establish a definition of symptom resolution. DESIGN, SETTING, AND PARTICIPANTS: In this diagnostic/prognostic study, psychometric properties of SE-C19 were assessed in participants recruited into an ongoing, adaptive, phase 1/2/3, randomized, double-blind, placebo-controlled clinical trial, during 2020 to 2022. Adult outpatients with symptomatic COVID-19 were randomized 1:1:1 to receive 2.4 g or 8.0 g intravenous casirivimab and imdevimab or placebo, in outpatient centers at 114 sites, from 2 countries (US and Mexico). MAIN OUTCOMES AND MEASURES: Reliability, validity, and sensitivity to change of the SE-C19 were assessed. SE-C19 and Patient Global Impression of Severity (PGIS) were administered daily from predose at day 1 to day 29. RESULTS: Analysis was conducted on 657 adult outpatients (342 female patients [52.1%], 562 White patients [85.5%]), and 337 non-Hispanic patients [51.3%]. At baseline, patients reported a mean (SD) of 6.6 (3.9) symptoms (ie, rated as at least mild) with a mean (SD) of 3.8 (3.3) of these symptoms being rated as moderate or severe. Stable patients according to PGIS showed scores with intraclass correlation values indicating moderate-to-good test-retest reliability (ie, 0.50-0.90). At baseline, 20 item scores (87%) varied significantly across PGIS-defined groups, supporting the validity of the SE-C19. A symptom-resolution end point was defined after excluding the item sneezing due to its low ability to discriminate severity levels, and excluding confusion, rash, and vomiting, due to their low prevalence in this population. Symptom resolution required complete absence of all remaining items, except cough, fatigue, and headache, which could be mild or moderate in severity. A total of 19 of 23 items from the SE-C19 instrument were identified as valid and reliable to measure disease-related symptoms in outpatients with COVID-19. CONCLUSIONS AND RELEVANCE: This study identified 19 items that are valid and reliable to measure disease-related symptoms in outpatients with COVID-19, and proposed a definition of symptom resolution for potential use in future clinical trials.