Measuring cough severity: development and pilot testing of a new seven-item cough severity patient-reported outcome measure

Abstract

Objective: Although chronic and subacute cough are clinically problematic and a target of therapeutic interventions, there are no validated cough severity patient-reported outcome (PRO) instruments for comprehensively evaluating cough severity in clinical trials. The Cough Severity Diary (CSD) is a simple, seven-item daily diary developed to meet this need. The objective of this study was to assess preliminary measurement characteristics in a small sample of patients with chronic or subacute cough. Methods: Thirty-nine patients (24 chronic; 15 subacute) participated in a two-week prospective pilot study. Patients completed the CSD each evening and validation instruments (cough severity visual analog scale [VAS], Leicester Cough Questionnaire [LCQ], Medical Outcomes Study 36-Item Short Form [SF-36], Work Productivity Index [WPAI], MOS Sleep Scale [MOS-SS]) at baseline, days 8 and 15, and a global rating of change at days 8 and 15. Results: Confirmatory factor analyses supported three severity subscales: frequency (three items), intensity (two items), and disruption (two items) (χ² = 10.57 (11)). For the CSD total score, internal consistency (α) on day 1 was 0.89, and on day 8 was 0.96; reproducibility (intraclass correlation coefficients [ICC]) was 0.68 on day 1 to day 8 and 0.94 on day 8 to day 15. CSD total scores correlated with the VAS (r = 0.84, p < 0.0001), LCQ total (r =-0.62, p < 0.0001) and subscale scores (r =-0.43, p < 0.01 to -0.60, p < 0.0001), and WPAI subscale scores (r = 0.27 (ns) to 0.51, p < 0.01). No significant relationships with SF-36 or MOS-SS were found. Subacute patients showed significant improvement over time (F = 3.20, p < 0.05). Conclusions: Results suggest that the CSD is ready for further testing in larger naturalistic studies or as an exploratory endpoint in clinical trials of patients with subacute or chronic cough.