Table 2. Risk factors for ≥4-fold increase in hemagglutination inhibition (HI) titer against A/Mexico/4108/2009(H1N1) from 2009 to 2010 among cohort subjects, Kamphaeng Phet, Thailand; odds ratios calculated by binary logistic regression.
| Variables | Total N | A/Mexico/4108/2009(H1N1) | ||
| ≥4-fold | Unadjusted OR (95% CI) | Adjusted OR (95% CI) | ||
| increase | ||||
| N (%) | ||||
| Birth Year | ||||
| >1968 | 195 | 25 (34.2) | 2.8 (1.5–5.3) | 2.2 (1.1–4.3) |
| 1958–1968 | 249 | 31 (42.5) | 2.7 (1.4–5) | 2.5 (1.3–4.8) |
| ≤1957 | 337 | 17 (23.3) | Reference | |
| Gender | ||||
| Male | 318 | 29 (39.7) | 1 (0.6–1.6) | - |
| Female | 463 | 44 (60.3) | ||
| Indoor Water | ||||
| Yes | 528 | 59 (80.8) | 2.1 (1.2–3.9) | - |
| No | 253 | 14 (19.2) | ||
| Geographical Region | ||||
| Phran Kratai District | 298 | 44 (60.3) | 2.7 (1.7–4.4) | 2.6 (1.5–4.5) |
| Mueng District | 483 | 29 (39.7) | Reference | |
| Swine Exposure | ||||
| Yes | 87 | 7 (9.6) | 0.8 (0.4–1.9) | - |
| No | 694 | 66 (90.4) | ||
| Developed a respiratory illness in the last 12 monthsa | ||||
| Yes | 423 | 44 (60.3) | 1.3 (0.8–2.2) | - |
| No | 357 | 29 (39.7) | ||
| A/Brisbane/59/2007(H1N1) | ||||
| Positive | 143 | 19 (26) | 1.7 (1.0–2.9) | - |
| Negative | 638 | 54 (74) | ||
| A/SW/Gent/7625/99(H1N2) | ||||
| Positive | 211 | 48 (65.8) | 6.4 (3.8–10.7) | 5.8 (3.4–10.0) |
| Negative | 570 | 25 (34.2) | Reference | |
| A/SW/Lutol/3/2000(H1N1) | ||||
| Positive | 26 | 11 (15.1) | 8.2 (3.6–18.6) | 3.7 (1.5–9.6) |
| Negative | 755 | 62 (84.9) | Reference | |
Abbreviation: OR, odds ratio; CI, confidence interval.
a
Covariate has some missing values.