Baseline characteristics according to hospitalisation for respiratory tract infection
| All patients | Never RTI | RTI | Test statistic | |
| No. of patients (% total) | 5677 | 5117 (90%) | 560 (10%) | – |
| Baseline smoking status, n (%) | ||||
| Never | 2288 (40%) | 2128 (42%) | 160 (29%) | – |
| Former | 1935 (34%) | 1720 (34%) | 215 (38%) | – |
| Current | 1454 (26%) | 1269 (25%) | 185 (33%) | Χ2 (2)=38, p=0.000 |
| % female | 67.8 | 68.6 | 61.1 | Χ2 (1)=13, p=0.000 |
| Median age (IQR) | 61.4 (51.2, 71.3) | 60.3 (50.2, 70.1) | 70.8 (62.6, 77.4) | KW (1)=245, p=0.0001 |
| Median BMI (IQR)* | 26.8 (23.8, 30.9) | 26.9 (23.8, 30.8) | 26.6 (23.7, 31.6) | KW (1)=0, p=0.92 |
| Townsend score quintile† | ||||
| 1 | 23.1 | 23.5 | 19.8 | – |
| 2 | 24 | 24.4 | 20.3 | – |
| 3 | 21.8 | 21.4 | 25 | – |
| 4 | 18.3 | 18 | 21.4 | – |
| 5 | 12.9 | 12.8 | 13.6 | Χ2 (4)=12.9, p=0.012 |
| Immunosuppressant DMARDs | 10 | 10.4 | 6.4 | Χ2 (1)=8.9, p=0.003 |
| Glucocorticoids | 16.7 | 15.6 | 27 | Χ2 (1)=46.9, p=0.000 |
| Type 2 diabetes | 10.7 | 10.4 | 13.6 | Χ2 (1)=5.2, p=0.022 |
| Asthma | 11.6 | 10.9 | 18 | Χ2 (1)=25.2, p=0.000 |
| COPD | 4.3 | 3.2 | 13.4 | Χ2 (1)=127.9, p=0.000 |
Never RTI=no hospitalised RTI during follow-up; RTI=at least one hospitalised RTI during follow-up. Figures are percentages, unless otherwise stated.
*33% missing BMI.
†0.5% missing SES.
RTI, respiratory tract infection; n, number; BMI, body mass index; DMARDs, disease-modifying antirheumatic drugs; COPD, chronic obstructive pulmonary disorder; Χ2, chi-squared test; KW, Kruskal-Wallis test; SES, socioeconomic status.