Force of Infection (FOI) in farms and during transport
There were in total 4,226 paired pig sera and nasal swabs collected from
swine originating from Guangdong, with 46 (1.09%) H3 viruses isolated
and 936 (22.1%) having antibody titers ≥1:40 (sero-positive) to H3 SIV
(Table 1). Among the 3,290 sero-negative samples, there were 40 (1.22%)
H3 viruses isolated. The mean weekly FOI λt during
transport for swine originating from Guangdong was estimated to be
0.0286 (95% CI = 0.0211-0.0391), while the weekly force of infection in
farms were λf = 0.0125 (95% CI = 0.0118-0.0134), 0.0089
(95% CI = 0.0084-0.0095), and 0.0069 (95% CI = 0.0065-0.0074)
respectively, assuming exposure durations of
20, 28 and 36 weeks in farms.
Hence, the relative FOI during transport was 229-414% of that in farms,
indicating a noticeable increased transmission intensity during
transportation comparing to that within farms.