Development and validation of the cough severity index: a severity index for chronic cough related to the upper airway.

Objectives/hypothesis: To develop and validate a cough severity index (CSI) which quantifies patients' symptoms associated with upper airway chronic cough and to provide a tool for treatment outcome measures.

Methods: Two hundred patients who had a complaint of chronic cough and/or dyspnea were given a 49- item questionnaire developed through a clinical consensus of the most common symptoms of chronic cough of upper airway origin. The instrument was reduced to 10 questions using statistical methodology. Fifty subsequent patients were given the CSI to measure test-retest reliability at two different moments in time. Twenty healthy controls (HC) were given the instrument to obtain validity. An additional 95 participants provided pre- and posttreatment outcomes using the CSI.

Results: Principle Component Analysis (PCA) revealed a single factor with the original 49 questions. A combination of PCA, rank-ordering item-total correlation and communality, as well as clinical consensus further reduced the questionnaire to 10 items. Internal consistency of the CSI was 0.97. Test-retest reliability was r = 0.83. An r = 0.60 for divergent validity between the CSI and the Cough-Specific Quality-of-Life Questionnaire (CQLQ) demonstrated two fairly separate instruments, although both measured cough. Mann-Whitney test was significant between symptomatic patients and healthy controls (P < 0.0004). The results of 20 HC showed a mean of 0.45 (standard deviation = 1.39). Results for treatment outcomes revealed significance with the Wilcoxon test (P < 0.0001) and paired samples t test showed significantly different correlations between pre- and postmeasures.

Conclusion: The CSI is a short, simple instrument that can be used in the clinical setting to quantify a patient's symptoms of chronic cough of upper airway origin. It represents a statistically reliable, valid, and clinically relevant instrument that can be used to measure treatment outcomes for chronic cough.