Characteristic | Influenza positive | Influenza negative | OR (95% CI) | P-value |
---|---|---|---|---|
N = 825 | N = 923 | |||
Age group, n (%) | ||||
15–19 years | 27 (3.3) | 42 (4.6) | 1 | |
20–24 years | 153 (18.6) | 214 (23.2) | 1.11 (0.66–1.88) | 0.692 |
25–29 years | 327 (39.6) | 341 (36.9) | 1.49 (0.90–2.48) | 0.122 |
30–34 years | 206 (25.0) | 214 (23.2) | 1.50 (0.89–2.52) | 0.128 |
35–39 years | 89 (10.8) | 94 (10.2) | 1.47 (0.84–2.59) | 0.178 |
40–44 years | 23 (2.8) | 18 (2.0) | 1.99 (0.91–4.35) | 0.086 |
Median age in years (range) | 28.5 (15–44) | 28 (15–44) | 1.02 (1.00–1.04) | 0.021 |
Underlying conditions, n (%) | ||||
One or more | 136 (16.5) | 106 (11.5) | 1.52 (1.16–1.99) | 0.003 |
Cardiovascular disease | 28 (3.4) | 23 (2.5) | 1.37 (0.78–2.40) | 0.268 |
Chronic obstructive pulmonary disease | 12 (1.5) | 8 (0.9) | 1.68 (0.69–4.14) | 0.256 |
Asthma | 10 (1.2) | 6 (0.7) | 1.87 (0.68–5.17) | 0.227 |
Diabetes a | 0 (0.0) | 3 (0.3) | 0.29 (0.00–2.71) | 0.294 |
Renal impairment | 68 (8.2) | 54 (5.9) | 1.44 (0.99–2.09) | 0.053 |
Cirrhosis | 9 (1.1) | 8 (0.9) | 1.26 (0.48–3.28) | 0.637 |
Neuromuscular a | 1 (0.1) | 0 (0.0) | 1.12 (0.03–∞) | 0.944 |
Neoplasm | 2 (0.2) | 2 (0.2) | 1.12 (0.16–7.95) | 0.912 |
Rheumatic disease a | 0 (0.0) | 1 (0.1) | 1.12 (0.00–43.63) | 1.000 |
Antiviral treatment before admission, n (%) | 8 (1.0) | 11 (1.2) | 0.81 (0.32–2.02) | 0.652 |
Influenza vaccination, n (%) | 3 (0.4) | 3 (0.3) | 0.99 (0.97–1.01) | 0.392 |
Trimester of pregnancy, n (%) | ||||
First (0–13 weeks) | 177 (21.5) | 221 (23.9) | 1 | |
Second (14–26 weeks) | 355 (43.0) | 372 (40.3) | 1.19 (0.93–1.52) | 0.162 |
Third (27–42 weeks) | 291 (35.3) | 325 (35.2) | 1.12 (0.87–1.44) | 0.388 |
Gestational age at admission (weeks), median (range) | 23 (1–41) b | 23 (3–42) c | 1.00 (0.99–1.01) | 0.872 |
Smoking habits, n (%) | ||||
Never smoked | 563 (68.2) | 602 (65.2) | 1 | |
Past smoker | 225 (27.3) | 268 (29.0) | 0.90 (0.73–1.11) | 0.317 |
Current smoker | 37 (4.5) | 53 (5.7) | 0.75 (0.48–1.15) | 0.188 |
Socioeconomic class, n (%) | ||||
Managerial | 359 (43.5) | 383 (41.5) | 1 | |
Skilled | 360 (43.6) | 425 (46.0) | 0.9 (0.74–1.10) | 0.324 |
Unskilled | 34 (4.1) | 52 (5.6) | 0.7 (0.44–1.10) | 0.121 |
Other | 72 (8.7) | 63 (6.8) | 1.22 (0.84–1.76) | 0.29 |
Time from onset of symptoms to swabbing, n (%) | ||||
0–2 days | 559 (67.8) | 541 (58.6) | 1 | |
3–4 days | 228 (27.6) | 280 (30.3) | 0.79 (0.64–0.97) | 0.027 |
5–7 days | 38 (4.6) | 102 (11.1) | 0.36 (0.24–0.53) | 0.001 |
Days from onset of symptoms to swabbing, median (range) | 2 (0–7) | 2 (0–7) | 0.87 (0.82–0.93) | 0.001 |