This assessment examined PRRSV outbreaks across 76 farrow to wean sites managed within a single production group and evaluated the biosecurity interventions in place at each. Sites without air filtration had 20 times greater odds of a PRRSV outbreak. Protection was strongest where air filtration and feed mitigation were both in place. Sites located outside Minnesota and Iowa carried 98.5 to 99 percent lower odds, which quantifies how much of the exposure is a function of regional pig density rather than of the individual site.
The filtration effect sits in a consistent line with the earlier field evidence. Dee and colleagues reported in 2012 that the odds of new PRRSV infection before filtration were 7.97 times higher than after, across 38 herds. Alonso and colleagues reported in 2013 an approximate 80 percent reduction in the risk of novel PRRSV introduction, comparing 20 filtered against 17 non filtered herds over seven years. Desrosiers and Cousin extended the picture in 2023 to 65 filtered farms, of which 95.4 percent remained PRRSV negative.
What this study adds is the interaction. The strongest result came from filtration combined with feed mitigation, not from either alone, and the location term shows that neither intervention removes the underlying regional exposure. For a producer, that supports a reading of filtration as one control within a programme whose other elements determine how much the filtration is able to deliver. For a designer, the location finding is a reminder that the case for a system is built on the exposure of the particular site rather than on a general figure.