Table 2. Odds ratios for elevated hemagglutination inhibition assay antibodies (enrollment sera) against swine influenza virus using proportional odds modeling*.
| Variables | n | Swine (H1N1) |
Swine (H1N2) |
|||
|---|---|---|---|---|---|---|
| Unadjusted OR (95% CI) | Adjusted OR† (95% CI) | Unadjusted OR (95% CI) | Adjusted OR† (95% CI) | |||
| AHS swine-exposed | 707 | 35.8 (8.7–146.8) | 54.9 (13.0–232.6) | 17.2 (7.9–37.7) | 13.5 (6.1-29.7) | |
| AHS nonswine-exposed | 80 | 10.6 (2.4–47.5) | 28.2 (6.1–130.1) | 4.7 (1.9–11.4) | 6.9 (2.8-17.2) | |
| University controls | 79 | Ref | Ref | Ref | Ref | |
| Age continuous |
866 |
1.00 (0.99–1.01) |
0.97 (0.96–0.98) |
|
1.02 (1.01–1.03) |
– |
| Sex | ||||||
| Male | 484 | 3.7 (2.8–4.9) | 3.3 (2.4–4.5) | 3.5 (2.7–4.5) | 3.0 (2.3-4.0) | |
| Female |
382 |
Ref |
Ref |
|
Ref |
Ref |
| Received flu shot in the past 4 y | ||||||
| Yes | 479 | 1.0 (0.8–1.3) | 1.4 (1.1–1.9) | 1.3 (1.0–1.7) | – | |
| No/unsure |
387 |
Ref |
Ref |
|
Ref |
– |
| Human influenza (H1N1) (titer >40) | ||||||
| Positive | 347 | 1.1 (0.9–1.4) | – | 1.6 (1.2–2.0) | 1.8 (1.4-2.4) | |
| Negative | 519 | Ref | – | Ref | Ref | |
*OR, odds ratio; CI, confidence interval; AHS, Agricultural Health Study; AHS swine-exposed, participants from the AHS who reported working in swine production; AHS nonswine-exposed, participants from the AHS who denied ever working in swine production, 94% were spouses of AHS swine-exposed; university controls, faculty, staff, and students from the University of Iowa who denied ever working in swine production. †Final multivariable models were designed that used a saturated model including all potential risk factors (see Methods) and manual backwards elimination.