Table 4.
Final Multivariable Model Results From Complete Cases With the Outcome of Seroconversions Against Swine H1N1 and Swine H3N2
| Risk Factor | Total n | Seroconverted, n (%) | OR (95% CI) | |
|---|---|---|---|---|
| Swine H1N1 | Type of swine exposure | |||
| Exposed to CAFO swine | 22 | 21 (95.5%) | 17.89 (3.12–342.01) | |
| Not exposed to CAFO swine | 94 | 50 (53.2%) | 0.89 (.44–1.82) | |
| Unexposed | 71 | 39 (54.9%) | Ref. | |
| Elevated MN titer at baseline (≥20)? | ||||
| Yes | 62 | 22 (35.5%) | 0.18 (.08–.37) | |
| No | 125 | 88 (70.4%) | Ref. | |
| Medication taken in the last 30 days? | ||||
| Yes | 47 | 21 (44.7%) | 0.45 (.20–.98) | |
| No | 140 | 89 (63.6%) | Ref. | |
| At least 1 respiratory infection among a household member in the last 12 months? | ||||
| Yes | 81 | 42 (51.9%) | 0.44 (.22–.89) | |
| No | 106 | 68 (64.2%) | Ref. | |
| Baseline H1N1-specific IgA titer (standardized) | ||||
| Mean (SD) | 0.36 (1.29) | 1.83 (1.08–4.49) | ||
| Swine H3N2 | Type of swine exposure | |||
| Exposed to CAFO swine | 22 | 14 (63.6%) | 2.16 (.78–6.20) | |
| Not exposed to CAFO swine | 94 | 32 (34.0%) | 0.55 (.27–1.10) | |
| Unexposed | 71 | 28 (39.4%) | Ref. | |
| Elevated MN titer at baseline (≥20)? | ||||
| Yes | 160 | 57 (35.6%) | 0.28 (.11–.68) | |
| No | 27 | 17 (63.0%) | Ref. | |
| Outbreak among animals in the last 30 days? | ||||
| Yes | 9 | 7 (77.8%) | 8.62 (1.87–61.79) | |
| No | 178 | 67 (37.6%) | Ref. |
Sera samples were collected from 116 participants who were exposed to swine and 71 who were not exposed to swine (unexposed) in the Shandong and Jiangsu provinces of China between March 2015 and December 2017. Swine-exposed participants were either enrolled at CAFO facilities (exposed to CAFO swine) or at non-CAFO facilities (not exposed to CAFO swine), including house-holding swine farms, abattoirs, a veterinary station, and an animal market. Samples were collected at each of 3 time points (0, 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. A multivariable logistic regression using empirical (sandwich) covariance estimates was used to adjust for repeated measures over time.Abbreviations: CAFO, confined animal feeding operations; CI, confidence interval; H1N1 or H2N2, swine influenza virus subtype; IgA, immunoglobin A; MN, microneutralization; OR, odds ratio; Ref., referent group; SD, standard deviation.