Background: The purpose of the current study was to determine the final content validation, psychometric characteristics, clinically meaningful improvement, and responder thresholds of the Clostridium difficile infection (CDI)-Daily Symptoms (CDI-DaySyms™) patient-reported outcome (PRO) questionnaire.
Methods: This validation study was part of two phase III studies (NCT01987895 and NCT01983683) conducted in patients with mild-to-moderate or severe CDI who completed the CDI-DaySyms™ daily throughout the treatment period. The questionnaire was evaluated in three stages: final PRO item content validation (Stage I); psychometric evaluation of reliability and construct validity (Stage II); and determination of clinically meaningful improvement and responder thresholds using distribution-based methods (Stage III).
Results: The analysis included 168 patients. Most patients were female and Caucasian with mild-to-moderate CDI. The mean age was 57.1 years. Initial item analysis supported by confirmatory factor analysis demonstrated the relevance of 10 items grouped into three distinct domains (Diarrhea Symptoms, Abdominal Symptoms, and Systemic/Other Symptoms). Domain scores demonstrated acceptable internal consistency and test-retest reliability, were sensitive to change, and correlated in expected directions with other relevant symptom and disease-severity measures. Responder thresholds were defined as score changes of - 1.00, - 0.80, and - 0.70 in the Diarrhea Symptoms, Abdominal Symptoms, and Systemic/Other Symptoms domains, respectively.
Conclusions: The CDI-DaySyms™ is a valid measure of patient-reported CDI symptoms, with good measurement properties, which supports its utility as an endpoint in clinical studies. Further studies confirming responder thresholds based on anchor-based methods are required.
Trial registration: NCT01987895 , registered November 20, 2013; NCT01983683 , registered November 14, 2013.
Keywords: Clostridium difficile infection; Clostridium difficile–associated diarrhea; Patient-reported outcomes; Psychometric validation; Symptoms.