Logistic regression analyses of the associations of the background disorders with sputum production

DisorderSubjects nAdjusted# OR (95% CI)p-value
Current asthma1023.04 (1.87–4.94)<0.001
Upper airway cough syndrome1571.32 (0.88–1.96)0.18
Gastro-oesophageal reflux disease1131.24 (0.80–1.92)0.34
Unexplained chronic cough1440.54 (0.36–0.81)0.003
Number of background disorders2711.62 (1.26–2.08)<0.001

For each disorder, the control group was those with chronic cough but without that background disorder. Several subjects had more than one background disorder. #: adjusted for current smoking; : the number of background disorders was calculated as the sum of current asthma, upper airway cough syndrome and gastro-oesophageal reflux disease; the odds ratio was calculated per one background disorder.