Risk factors associated with seropositivity to porcine respiratory coronavirus in Danish swine herds

To determine risk factors associated with the introduction of porcine respiratory coronavirus (PRCV) to Denmark, a cross-sectional study of 408 swine herds was carried out between May 1985 and June 1986. The association between herd-PRCV serological status and possible risk factors, obtained from a field questionnaire, was assessed by unconditional maximum likelihood logistic regression. An increasing herd size, location in the Jutland peninsula compared with location on the island of Funen (OR=7.9 in a multivariable logistic regression model not including interaction terms), the presence of a slurry system (i.e. pigs living on a slatted floor, OR=4.6) and purchase of pigs (OR=1.7) were significantly associated with seropositivity. Two significant interactions, both involving herd size, were subsequently identified. The PRCV serological status of neighbouring herds was found to be related, and closeness of a seropositive herd was associated with an increased risk of a herd being serologically positive.