Table 1 Characteristics of cases and controls
Laboratory confirmed influenza cases | Test-negative controls | ||
|---|---|---|---|
n (%) | n (%) | p-value | |
Total | 303 (100) | 286 (100) | |
Age groups (years) | 0.004 | ||
< 5 | 10 (3.3) | 9 (3.1) | |
5 - 14 | 38 (12.4) | 19 (6.6) | |
15 - 44 | 174 (57.4) | 151 (52.8) | |
45 - 64 | 65 (21.5) | 69 (24.1) | |
65 - 79 | 13 (4.3) | 26 (9.1) | |
≥ 80 | 3 (1.0) | 12 (4.2) | |
Sex | 0.387 | ||
Male | 146 (48.2) | 148 (51.7) | |
Female | 157 (51.8) | 138 (48.3) | |
Residence | 0.943 | ||
Rural | 43 (14.2) | 40 (14.0) | |
Urban | 260 (85.9) | 246 (86.0) | |
Major chronic conditions | 0.005 | ||
0 | 232 (76.5) | 199 (69.6) | |
1 | 59 (19.5) | 56 (19.6) | |
> 1 | 12 (4.0) | 31 (10.8) | |
Outpatient visits in the previous year | 0.047 | ||
0 | 53 (17.5) | 33 (11.5) | |
1 to 4 | 134 (44.2) | 120 (42.0) | |
> 4 | 116 (38.3) | 133 (46.5) | |
Health care setting | <0.001 | ||
Primary health care | 290 (95.7) | 240 (83.9) | |
Hospital | 13 (4.3) | 46 (16.1) | |
Period | <0.001 | ||
Week 43 to 46/2010 | 5 (1.7) | 40 (14.0) | |
Week 47 to 50/2010 | 6 (1.9) | 18 (6.3) | |
Week 51/2010 to 2/2011 | 192 (63.4) | 101 (35.3) | |
Week 3 to 6/2011 | 81 (26.7) | 95 (33.2) | |
Week 7 to 12/2011 | 19 (6.3) | 32 (11.2) | |
Delay between symptom onset and swabbing | 0.118 | ||
≤4 days | 297 (98.0) | 274 (95.8) | |
>4 days | 6 (2.0) | 12 (4.2) | |
Pandemic influenza vaccine 2009-2010 | 0.001 | ||
No | 297 (98.0) | 260 (90.9) | |
Yes | 6 (2.0) | 26 (9.1) | |
Seasonal influenza vaccine 2010-2011 | <0.001 | ||
No | 290 (95.7) | 241 (84.3) | |
Yes | 13 (4.3) | 45 (15.7) |