Validity and reliability of the COVID-19 symptom index, an instrument evaluating severity of general and otolaryngological symptoms

Background: There is no clinical instrument evaluating symptoms of COVID-19. Objective: To develop a clinical instrument for evaluating symptoms of COVID-19 mild-to-moderate forms. Methods: COVID-19 patients were recruited from EpiCURA Hospital (Belgium). They completed the COVID-19 Symptom Index (CSI) twice to assess the test-retest reliability. The internal consistency was evaluated with Cronbach’s alpha. CSI was completed by healthy subjects to assess the internal validity. Patients completed CSI 6 weeks after the COVID-19 resolution to evaluate the responsiveness to change. Results: Ninety-four COVID-19 patients and 55 healthy individuals completed the evaluations. Symptoms associated with the higher severity score were fatigue, headache and myalgia. The Cronbach’s alpha value was 0.801, indicating high internal consistency. The test-retest reliability was adequate (rs = 0.535, p =.001). The correlation between CSI total score and SNOT-22 was high (rs = 0.782; p <.001), supporting a high external validity. COVID-19 patients reported significant higher CSI score than healthy individuals, suggesting an adequate internal validity. The mean CSI significantly decreased after the COVID-19 resolution, supporting a high responsiveness to change property. Conclusion and significance: The CSI is a reliable and valid patient reported outcome questionnaire for the evaluation of symptom severity of COVID-19 patients.