Table 3.
Predicted Probabilities of Seroconversion and Geometric Mean Titers Over Time for Swine H1N1 and Swine H3N2
| Predicted Probability (95% CI) | OR (95% CI) | Baseline Titer Geometric Mean (σ) | 12-Month Titer Geometric Mean (σ) |
24-Month Titer Geometric Mean (σ) | ||
|---|---|---|---|---|---|---|
| Swine H1N1 | Exposed to CAFO swine | 0.19 (.15–0.25) | 1.30 (.86–1.97) | 10.11 (2.97) | 34.29 (3.89) | 60.25 (2.71) |
| Not exposed to CAFO swine | 0.13 (.11–.15) | 0.83 (.60–1.14) | 12.39 (3.27) | 34.29 (3.53) | 30.67 (2.75) | |
| Unexposed | 0.15 (.12–.19) | Ref | 10.28 (2.66) | 22.90 (2.88) | 26.03 (2.77) | |
| Swine H3N2 | Exposed to CAFO swine | 0.11 (.08–.16) | 0.87 (.52–1.47) | 38.28 (3.32) | 62.29 (2.33) | 32.08 (3.25) |
| Not exposed to CAFO swine | 0.06 (.04–.08) | 0.44 (.28–.70) | 43.56 (3.49) | 47.87 (2.78) | 42.43 (3.15) | |
| Unexposed | 0.13 (.10–.17) | Ref | 75.68 (3.16) | 67.67 (2.71) | 73.27 (3.84) |
Sera samples were collected from 658 participants in the Shandong and Jiangsu provinces of China between March 2015 and December 2017. Participants were grouped into 3 categories: (1) swine-exposed and enrolled at CAFO (exposed to CAFO swine); (2) swine-exposed and enrolled at sites other than CAFO (not exposed to CAFO); and (3) not swine-exposed (unexposed). Non-CAFO sites included house-holding swine farms, abattoirs, a veterinary station, and an animal market. Samples were collected at 0 (baseline), 12, and 24 months, with additional acute and convalescent sera samples collected at individually reported influenza-like illness events between follow-up visits. Seroconversion against each virus was defined as a 4-fold rise in titer, relative to any previously gathered sample, and 1 titer value ≥40. Predicted probabilities and ORs were calculated from a univariate logistic regression model using empirical (sandwich) covariance estimates to adjust for repeated measurements within individuals over time.Abbreviations: σ, standard deviation; CAFO, confined animal feeding operations; CI, confidence interval; H1N1 or H2N2, swine influenza virus subtype; OR, odds ratio; Ref., referent group.