Swine Workers and Swine Influenza Virus Infections
Gregory C. Gray,* Troy McCarthy,* Ana W. Capuano,* Sharon F.
Setterquist,* Christopher W. Olsen,† Michael C. Alavanja,‡ and Charles F.
Lynch*
*University of Iowa College of Public Health, Iowa City,
Iowa, USA; †University of Wisconsin-Madison School of Veterinary Medicine,
Madison, Wisconsin, USA; and ‡National Cancer Institute, Bethesda, Maryland,
USA
Vol. 13, No. 12 • December 2007
| Appendix Table. Risk factor analyses for an increase in antibody titer (at any point from enrollment to 24–month follow-up) against swine influenza virus among AHS participants* | |||||||||||
| Variables | Total sample |
Swine influenza (H1N1), 4-fold increase† |
Swine influenza (H1N1), greatest increase‡ |
||||||||
n (%) |
Unadjusted OR (95% CI) |
Adjusted OR (95% CI) |
2-fold, n (%) |
4-fold, n (%) |
6-fold, n (%) |
>8-fold, n (%) |
Unadjusted OR (95% CI) |
Adjusted OR (95% CI) |
|||
| Age (continuous) | 726 |
180 (24.8) |
1 (0.98–1.01) |
– |
226 (31.1) |
128 (17.6) |
37 (5.1) |
15 (2.1) |
1 (0.98–1.01) |
– |
|
| Sex | |||||||||||
| Male | 419 |
129 (30.8) |
2.2 (1.6–3.2) |
2.2 (1.6–3.2) |
144 (34.4) |
96 (22.9) |
23 (5.5) |
10 (2.4) |
2.3 (1.8–3.1) |
2.3 (1.8–3.1) |
|
| Female | 307 |
51 (16.6) |
Ref |
Ref |
82 (26.7) |
32 (10.4) |
14 (4.6) |
5 (1.6) |
Ref |
Ref |
|
| Exposure to swine during follow-up | |||||||||||
| Swine exposure | |||||||||||
| AHS swine-exposed at enrollment | 650 |
171 (26.3) |
2.6 (1.3–5.4) |
– |
204 (31.4) |
123 (18.9) |
33 (5.1) |
15 (2.3) |
2 (1.3–3.2) |
– |
|
| AHS nonswine-exposed at enrollment | 75 |
9 (12) |
Ref |
– |
22 (29.3) |
5 (6.7) |
4 (5.3) |
0 (0) |
Ref |
– |
|
| Exposure to swine during follow-up | |||||||||||
| Exposed | 339 |
92 (27.1) |
1.3 (0.9–1.8) |
– |
113 (33.3) |
69 (20.4) |
15 (4.4) |
8 (2.4) |
1.3 (1–1.7) |
– |
|
| Not exposed | 387 |
88 (22.7) |
Ref |
– |
113 (29.2) |
59 (15.3) |
22 (5.7) |
7 (1.8) |
Ref |
– |
|
| Use of gloves when working with pigs | |||||||||||
| Never wears gloves | 102 |
25 (24.5) |
1 (0.6–1.6) |
– |
23 (22.6) |
19 (18.6) |
4 (3.9) |
2 (2) |
0.7 (0.5–1.1) |
– |
|
| Not exposed to pigs or exposed to pigs and wears gloves at least sometimes | 624 |
155 (24.8) |
Ref |
– |
203 (32.5) |
109 (17.5) |
33 (5.3) |
13 (2.1) |
Ref |
– |
|
| No. of pigs on farm‡ | |||||||||||
| <400 | 463 |
120 (25.9) |
2.2 (1.2–4.3) |
– |
149 (32.2) |
85 (18.4) |
25 (5.4) |
10 (2.2) |
1.9 (1.2–3) |
– |
|
| >400 | 174 |
48 (27.6) |
2.4 (1.2–4.9) |
– |
51 (29.3) |
36 (20.7) |
8 (4.6) |
4 (2.3) |
1.9 (1.2–3.1) |
– |
|
| Never directly exposed to pigs | 89 |
12 (13.5) |
Ref |
– |
26 (29.2) |
7 (7.9) |
4 (4.5) |
1 (1.1) |
Ref |
– |
|
| Works with nursery pigs§ | |||||||||||
| Yes | 559 |
131 (23.4) |
1.3 (0.9–1.9) |
– |
164 (29.3) |
93 (16.6) |
29 (5.2) |
9 (1.6) |
1.5 (1.1–2.1) |
– |
|
| No | 723 |
178 (24.6) |
Ref |
– |
225 (31.1) |
126 (17.4) |
37 (5.1) |
15 (2.1) |
Ref |
– |
|
| Works with finishing pigs§ | |||||||||||
| Yes | 262 |
73 (27.9) |
1.3 (0.9–1.9) |
– |
91 (34.7) |
54 (20.6) |
12 (4.6) |
7 (2.7) |
1.4 (1.1–1.9) |
– |
|
| No | 461 |
105 (22.8) |
Ref |
– |
134 (29.1) |
72 (15.6) |
25 (5.4) |
8 (1.7) |
Ref |
– |
|
| Flu vaccination | |||||||||||
| Vaccinated at least 1 of last 2 winters but otherwise not since 2001 | 168 |
38 (22.6) |
0.8 (0.5–1.3) |
– |
58 (34.5) |
22 (13.1) |
14 (8.3) |
2 (1.2) |
1 (0.7–1.4) |
– |
|
| Vaccinated at least 1 of last 2 winters and at least once other time since 2001 | 183 |
46 (25.1) |
0.9 (0.6–1.5) |
– |
61 (33.3) |
35 (19.1) |
8 (4.4) |
3 (1.6) |
1 (0.7–1.4) |
– |
|
| Vaccinated at least once since 2001 but not last winter | 98 |
27 (27.6) |
1.1 (0.6–1.8) |
– |
22 (22.5) |
22 (22.5) |
3 (3.1) |
2 (2) |
0.8 (0.5–1.3) |
– |
|
| Vaccinated before 2001 but none since | 50 |
9 (18) |
0.6 (0.3–1.3) |
– |
16 (32) |
6 (12) |
2 (4) |
1 (2) |
0.7 (0.4–1.3) |
– |
|
| No/unknown | 227 |
60 (26.4) |
Ref |
– |
69 (30.4) |
43 (18.9) |
10 (4.4) |
7 (3.1) |
Ref |
– |
|
| Human antibody titer to (H1N1) | |||||||||||
| >4-fold increase | 32 |
9 (28.1) |
1.2 (0.5–2.6) |
– |
9 (28.1) |
6 (18.8) |
2 (6.3) |
1 (3.1) |
1.1 (0.6–2.1) |
– |
|
| <4-fold increase | 694 |
171 (24.6) |
Ref |
– |
217 (31.3) |
122 (17.6) |
35 (5) |
14 (2) |
Ref |
– |
|
| *AHS, Agricultural Health Study; OR, odds ratio; CI, confidence interval; Ref, Ref. Final multivariable models were designed using a saturated model with all the variables included in this table, and manual backwards elimination. | |||||||||||
| †Binary logistic regression modeling. a 4-fold increase at any time from enrollment to 24-month follow-up, among participants who permitted sera collections at least 2 times during the study. | |||||||||||
| ‡Proportional odds modeling. The maximum increase in antibody titers from enrollment to 24-month follow–up, for each participant who permitted sera collections at least 2 times during the study. Grouping upper antibody titer levels when sparse, not to reject model assumption with the proportional odds score test. Greatest number of animals on farm during follow-up years. | |||||||||||
| §Based upon enrollment questionnaire. Summary counts that do not add up to 726 reflect missing data. | |||||||||||
This page posted November 29, 2007
This page last reviewed November 29, 2007
