J. Flori et al., RISK-FACTORS ASSOCIATED WITH SEROPOSITIVITY TO PORCINE RESPIRATORY CORONAVIRUS IN DANISH SWINE HERDS, Preventive veterinary medicine, 25(1), 1995, pp. 51-62
Serological screening of swine herds in 1984 indicated that porcine re
spiratory coronavirus (PRCV) had been introduced into Denmark. To dete
rmine risk factors associated with the introduction of PRCV, a cross-s
ectional study of 408 Danish swine herds was carried out between May 1
985 and June 1986. The association between herd-PRCV serological statu
s and possible risk factors, obtained from a field questionnaire, was
assessed by unconditional maximum likelihood logistic regression. An i
ncreasing 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 pur
chase of pigs (OR = 1.7) were significantly (P < 0.05) associated with
seropositivity. Two significant interactions, both involving herd siz
e, were subsequently identified. The PRCV serological status of neighb
ouring herds was found to be related, and closeness of a seropositive
herd was associated with an increased risk of a herd being serological
ly positive. The results of this study indicate that herd size may be
an important determinant of airborne transmission of PRCV infection, a
nd that herd size may modify the effect of other risk factors.