Table 2.
Microneutralization Assay Seroconversions Against Influenza A Viruses
| Influenza A Subtype | n (Unadjusted %/Adjusted % of total n = 658) | Unadjusted OR (95% CI) | Adjusted OR (95% CI) |
|---|---|---|---|
| A/swine/Guangdong/SSI/2012(H1N1) | 167 (25.4/14.3) | … | … |
| Exposed | 121 (23.2/13.9) | 0.60 (.40–.90) | 0.72 (.55–.94) |
| Unexposed | 46 (33.6/15.4) | Ref. | Ref. |
| A/swine/Guangdong/L22/2010(H3N2) | 97 (14.7/8.3) | … | … |
| Exposed | 62 (11.9/7.1) | 0.39 (.25–.63) | 0.49 (.36–.65) |
| Unexposed | 35 (25.6/11.7) | Ref. | Ref. |
| A/chicken/Jiangsu/WXWA021/2013(H9N2) | 4 (0.6/0.3) | … | … |
| Exposed | 3 (0.6/0.3) | 0.79 (.08–7.63) | 0.91 (.24–3.46) |
| Unexposed | 1 (0.7/0.3) | Ref. | Ref. |
| A/chicken/Jiangsu/WXBING2/2014(H5N6) | 2 (0.3/0.2) | … | … |
| Exposed | 1 (0.2/0.1) | 0.26 (.02–4.21) | 0.34 (.07–1.69) |
| Unexposed | 1 (0.7/0.3) | Ref. | Ref. |
| A/Jiangsu/Wuxi04/2013(H7N9) | 1 (0.2/0.1) | … | … |
| Exposed | 1 (0.2/0.1) | … | … |
| Unexposed | 0 (0.0/0.0) | … | … |
| A/chicken/Jiangsu/WX927/2013(H5N1) | 0 (0.0/0.0) | … | … |
| Exposed | 0 (0.0/0.0) | … | … |
| Unexposed | 0 (0.0/0.0) | Ref. | Ref. |
| Total seroconversions | 271 (41.2/23.2) | 0.37 (.25–.54) | 0.36 (.26–.48) |
| Total participants | 207 (31.5/17.7) | 0.47 (.32–.69) | 0.54 (.41–.70) |
Data are stratified by swine-exposed (exposed) and non–swine exposed (unexposed) participants. Sera samples were collected from 658 exposed (n = 521) and unexposed (n = 137) participants in the Shandong and Jiangsu provinces of China between March 2015 and December 2017. Samples were collected at 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. For unadjusted results, the number of participants in the cohort was used in the denominator. For adjusted results, the number of follow-up visits was used in the denominator as a proxy for person-time at risk (eg, a participant observed at baseline, 12 months, and 24 months had 2 person-years in the denominator, while a participant observed only at baseline and 12 months had 1 person-year in the denominator). Total seroconversions data are the sum of all seroconversion events. Total participants data are the number of participants who experienced at least 1 seroconversion event against any virus.Abbreviations: CI, confidence interval; OR, odds ratio; Ref., referent group.