Flock-level seroprevalence of and risk factors for infectious bronchitis virus in Korean laying-hen flocks.

Although there is circumstantial evidence that infectious bronchitis (IB) in the Korean layer industry has contributed to severe economic losses, the seroprevalence against IB virus (IBV) and risk factors associated with seropositivity are not well known. During May to October 2007, 820 blood samples were randomly collected from 41 laying hen flocks (20 birds in each flock) with ≥ 3,000 birds of 18 week of age or older in three provinces of Korea. The samples size was determined considering a flock-size range of 3,000?65,000 birds, an expected bird-level seroprevalence of ≥ 15%, and a 95% level of confidence. Serum samples were examined using a hemagglutination inhibition test for antibodies to IBV. The overall apparent flock-level seroprevalence was 46.3% (95% CI, 31.1?66.6) with no statistically significant differences among provinces (X = 1.205, p > 0.05). There were 19 positive flocks with one to eight seropositive birds, and 11 of these had one or two seropositive birds. None of the measured parameters were significantly associated with seropositivity against IBV in a subsequent multivariable logistic regression analysis. A longitudinal risk factor studies considering management and vaccination characteristics possibly associated with the IBV flock prevalence would be beneficial.