Table 1.
Recruitment of cases and controls by center
| Center | Asthma | Chronic rhino-sinusitis | Asthma and chronic rhino-sinusitis | Controls | Total |
|---|---|---|---|---|---|
| Umea | 117 | 41 | 29 | 168 | 355 |
| Uppsala | 114 | 42 | 32 | 202 | 390 |
| Stockholm | 101 | 26 | 34 | 232 | 393 |
| Gothenburg | 66 | 9 | 20 | 53 | 148 |
| Helsinki | 31 | 18 | 13 | 105 | 167 |
| Odense | 88 | 45 | 17 | 202 | 352 |
| Lodz | 23 | 27 | 5 | 111 | 166 |
| Katowice | 4 | 5 | 4 | 26 | 39 |
| London | 32 | 8 | 6 | 58 | 104 |
| Southampton | 32 | 3 | 5 | 33 | 73 |
| Amsterdam | 35 | 42 | 8 | 126 | 211 |
| Ghent | 17 | 28 | 13 | 88 | 146 |
| Brandenburg | 34 | 18 | 6 | 113 | 171 |
| Duisburg | 25 | 24 | 13 | 133 | 195 |
| Skopje | 5 | 14 | 3 | 95 | 117 |
| Palermo | 5 | 3 | 4 | 34 | 46 |
| Coimbra | 49 | 46 | 32 | 137 | 264 |
| Total | 778 | 399 | 244 | 1916 | 3337 |
Asthma cases had both a self-reported diagnosis of asthma and a history of either wheezing, shortness of breath or waking at night with breathlessness within the previous 12 months.
Chronic rhino-sinusitis cases were participants reporting at least two of these symptoms; 1) nasal blockage, 2) nasal discharge, 3) facial pain or pressure, or 4) reduced sense of smell, at least one of which had to be either blockage or discharge and symptoms had to have been present at least for 12 weeks without remission.
The controls lived in the same area but met neither of the criteria for diagnosis of asthma or sinusitis as above.