Multivariable logistic regression on H3-SIV
Of the 6,532 paired nasal swabs and pig sera collected over the study
period, 65% of the swine originated from Guangdong province, followed
by Jiangxi (17%), with relatively fewer isolates from other provinces
(Table 1). We isolated 63 H3N2 viruses from swabs and H3N2 antibodies
were detected in 1,340 pigs (Table 1), with 7 pigs having both virus
isolates and antibodies. Samples collected from farms (n = 5,832) which
provided ≥20 samples were included in our logistic regression.
Multivariable logistic regression was fitted to explain H3-subtype virus
infections (Table 2).
In the multivariable logistic regression model (Table 2), pigs with
anti-H3 HAI titers ≥1:40 were significantly associated (adjusted OR
[aOR] = 0.33, p = 0.012) with a lower risk of H3 virus detection in
the abattoir (i.e. presumed infection during transportation). This
reflected the protection against infection provided by the humoral
immune response. Swine from source farms with high H3 seroprevalence
(>30%) showed significantly higher H3 virus isolation
rates (aOR = 2.24, p-value = 0.015). No significant difference was
observed in the virus isolation among pigs with different length of stay
at the slaughterhouse and transport distance.