Table 1.
Characteristics of influenza laboratory confirmed cases (n = 331) and test-negative controls (n = 995) in the surveillance-based studya, season 2009-2010, Spain
| Characteristics | Cases n (%) |
ILI negative controls n (%) |
p valueb |
|---|---|---|---|
| Mean age (SDc) | 23.4 (17.8) | 25.4 (21.4) | 0.125 |
| Sex: male | 162/330 (49.1) | 492/984 (50.0) | 0.775 |
| Pandemic influenza vaccination | 9/331 (2.7) | 41/995 (4.1) | 0.234 |
| Seasonal influenza vaccination | 37/330 (11.2) | 104/988 (10.5) | 0.727 |
| Symptoms: | |||
| ▪ sudden onset | 211/241 (87.5) | 562/817 (68.8) | < 0.0001 |
| ▪ fever | 321/328 (97.9) | 890/991 (89.8) | < 0.0001 |
| ▪ malaise | 268/315 (85.1) | 713/967 (73.7) | < 0.0001 |
| ▪ headache | 251/320 (78.4) | 588/964 (61.0) | < 0.0001 |
| ▪ myalgia | 213/322 (66.2) | 589/978 (60.2) | 0.057 |
| ▪ cough | 295/329 (89.7) | 775/985 (78.7) | < 0.0001 |
| ▪ sore throat | 224/322 (69.6) | 601/970 (61.9) | 0.013 |
| ▪ shortness of breath | 27/305 (8.9) | 84/948 (8.9) | 0.996 |
| At least one chronic condition | 39/247 (15.8) | 120/826 (14.5) | 0.624 |
| Pregnancy | 5/329 (1.5) | 7/976 (0.7) | 0.187 |
| Complying with EU case definition | 195/331 (58.9) | 506/995 (50.8) | 0.011 |
| Delay onset-swabbing less than four days | 301/331 (90.9) | 874/995 (87.8) | 0.124 |
a Cases and controls recruited between week 48/2009 and week 8/2010, and with a delay symptom onset-swabbing less than eight days; b Chi-square or Fisher exact test when appropriate; c SD-standard deviation.