Table 1. Baseline characteristics of laboratory-confirmed influenza cases and test-negative controls, seasons 2003/04 through 2013/14, Netherlands.
| Variable | Cases (Number/Total (%)) | Controls (Number/Total (%)) | P-Value* |
|---|---|---|---|
| Seasonal vaccination received | 197/1422 (14·8) | 754/3410 (22·1) | <0·001 |
| 03/04 | 6/34 (17·6) | 21/79 (26·6) | |
| 04/05 | 22/73 (30·1) | 37/149 (24·8) | |
| 05/06 | 14/110 (12·7) | 44/278 (15·8) | |
| 06/07 | 10/94 (10·6) | 73/309 (23·6) | |
| 07/08 | 13/191 (6·8) | 64/417 (15·3) | |
| 08/09 | 21/197 (10·7) | 78/461 (16·9) | |
| 09/10 | 8/33 (24·2) | 92/289 (31·8) | |
| 10/11 | 27/246 (11·0) | 81/346 (23·4) | |
| 11/12 | 15/81 (18·5) | 91/434 (21·0) | |
| 12/13 | 53/311 (17·0) | 82/332 (24·7) | |
| 13/14 | 8/52 (15·4) | 91/316 (28·8) | |
| Gendera | 0·089 | ||
| Male | 683/1412 (48·4) | 1544/3380 (45·7) | |
| Female | 729/1412 (51·6) | 1836/3380 (54·3) | |
| Age group | <0·001 | ||
| 0–4 years | 128/1422 (9·0) | 503/3410(14·8) | |
| 5–14 years | 263/1422 (18·5) | 364/3410 (10·7) | |
| 15–59 years | 886/1422 (62·3) | 2009/3410 (58·9) | |
| ≥ 60 years | 145/1422 (10·2) | 534/3410 (15·7) | |
| Diagnosis | <0·.001 | ||
| ILI | 1142/1422 (80·3) | 1827/3410 (53·6) | |
| ARI | 280/1422 (19·7) | 1583/3410 (46·4) | |
| Interval from symptom onset to swab date, days | <0·001 | ||
| <3 d | 523/1422 (36·8) | 1193/3410 (35·0) | |
| 3–5 d | 776/1422 (54·6) | 1743/3410 (51·1) | |
| >5 d | 123/1422 (8·6) | 474/3410 (13·9) | |
| Chronic condition by age | 95/1422 (6·7) | 380/3410 (11·1) | <0·001 |
| 0–4 years | 3/95 (3·2) | 14/380 (3·7) | |
| 5–14 years | 5/95 (5·3) | 23/380 (6·0) | |
| 15–59 years | 56/95 (58·9) | 182/380 (47·9) | |
| ≥ 60 years | 31/95 (32·6) | 161/380 (42·4) | |
| Respiratory allerg by ageb | 114/1422 (8·0) | 248/3410 (7·3) | 0·374 |
| 0–4 years | 5/114 (4·4) | 15/248 (6·1) | |
| 5–14 years | 25/114 (21·9) | 38/248 (15·3) | |
| 15–59 years | 72/1114 (63·2) | 159/248 (64·1) | |
| ≥ 60 years | 12/114 (10·5) | 36/248 (14·5) | |
| Seasonal vaccination by age | 198/1430(13·8) | 883/3410 (22·1) | <0·001 |
| 0–4 years | 5/128 (3·9) | 41/566 (7·2) | |
| 5–14 years | 13/264 (4·9) | 28/403 (6·9) | |
| 15–59 years | 96/892 (10·8) | 357/2290 (15·6) | |
| ≥ 60 years | 84/146 (57·5) | 457/622 (73·5) |
*Statistically significant at P < 0·05
a Number of missing = 40
bNumber of missing = 50