A retrospective study of risk factors for porcine reproductive and respiratory syndrome virus infection and clinical disease in swine herds in Illinois during the early years of the pandemic

Objectives: To determine whether purchase and isolation of gilts and boars, purchase of semen for artificial insemination (AI), sharing of boars with other herds, herd size, and confinement housing were risk factors for porcine reproductive and respiratory syndrome (PRRS) virus infection and clinical PRRS in swine herds during the early years of the pandemic. Methods: A herd demographic and management survey of 103 swine herds in Illinois was conducted in 1992 and repeated in 1997 to determine whether PRRS virus infection and clinical disease had been diagnosed during the intervening period. Multivariable logistic regression analysis was conducted to identify risk factor associations. Results: Larger herd size was associated with an increased risk, and isolation of purchased gilts with a decreased risk, of both PRRS virus infection and clinical PRRS. Purchase of semen for AI was associated with an increased risk of PRRS virus infection. Implications: Swine producers should certify that purchased semen is free of PRRS virus, gilts should be isolated prior to introduction to the herd, and biosecurity measures should be implemented to prevent PRRS virus infection, particularly in larger herds.