| Number (%)with symptoms | Change in symptoms* | |||||
| Baseline | Follow-up | Number reduced | Number increased | Number no change | p Value† | |
| (A) Non-smokers (n = 57) | ||||||
| Respiratory symptoms | ||||||
| Median number of symptoms (IQR) | 1 (0–2) | 0 (0–2) | 19§ | 11§ | 25 | 0.142‡ |
| Any symptom | 31 (54) | 22 (39) | 14 | 5 | 38 | 0.147 |
| Wheezing/whistling | 14 (25) | 12 (21) | 9 | 7 | 41 | 0.402 |
| Shortness of breath | 13 (23) | 11 (20) | 9 | 7 | 39 | 0.402 |
| Cough, morning | 13 (23) | 7 (12) | 8 | 2 | 47 | 0.055 |
| Cough, rest of day or night | 20 (35) | 13 (23) | 13 | 6 | 38 | 0.084 |
| Phlegm production | 18 (32) | 8 (14) | 13 | 3 | 41 | 0.011 |
| Sensory symptoms | ||||||
| Median number of symptoms | 2 (0–2) | 1 (0–2) | 22§ | 12§ | 23 | 0.053‡ |
| Any symptom | 42 (74) | 34 (60) | 11 | 3 | 43 | 0.196 |
| Eyes, red or irritated | 25 (44) | 10 (18) | 18 | 3 | 36 | 0.001 |
| Nose, runny or sneezing | 31 (54) | 29 (51) | 10 | 8 | 39 | 0.407 |
| Throat, sore or scratchy | 27 (47) | 21 (37) | 15 | 9 | 33 | 0.154 |
| (B) Non-smokers who did not report a cold at either baseline or follow-up (n = 36) | ||||||
| Respiratory symptoms | ||||||
| Median number of symptoms | 0.5 (0–2.5) | 0 (0–1) | 10§ | 5§ | 19 | 0.163‡ |
| Any symptom | 18 (50) | 12 (33) | 7 | 1 | 28 | 0.232 |
| Wheezing/whistling | 9 (25) | 5 (14) | 5 | 1 | 30 | 0.109 |
| Shortness of breath | 8 (22) | 6 (18) | 5 | 3 | 26 | 0.363 |
| Cough, morning | 8 (22) | 4 (11) | 4 | 0 | 32 | 0.062 |
| Cough, rest of day or night | 11 (31) | 8 (22) | 7 | 4 | 25 | 0.274 |
| Phlegm production | 12 (33) | 5 (14) | 8 | 1 | 27 | 0.02 |
| Sensory symptoms | ||||||
| Median number of symptoms | 1 (0–2) | 0 (0–1) | 15§ | 7§ | 14 | 0.04‡ |
| Any symptom | 23 (64) | 15 (42) | 10 | 2 | 24 | 0.098 |
| Eyes, red or irritated | 14 (39) | 4 (11) | 11 | 1 | 24 | 0.003 |
| Nose, runny or sneezing | 15 (42) | 13 (36) | 7 | 5 | 24 | 0.387 |
| Throat, sore or scratchy | 16 (44) | 9 (25) | 11 | 4 | 21 | 0.059 |
*Reduction: symptoms at baseline, none at follow-up; increase: no symptoms at baseline, symptoms at follow-up; †the p value relates to the McNemar test for matched pairs, with exact probabilities based on a binomial assumption with the exception of ‡which relates to the Wilcoxon–Mann–Whitney test; §reduction: fewer symptoms at follow-up; increase: more symptoms at follow-up. IQR, interquartile range.