Four filtration approaches were tested against PRRSV aerosol transmission in a controlled challenge, ten replicates each. Transmission occurred in none of the ten HEPA replicates, none of the ten using a 95 percent DOP 0.3 micron filter, two of ten using bag filtration alone, four of ten using low cost filtration, and all ten controls. The HEPA arrangement combined a pre-filter screen, an EU8 bag filter and an EU13 HEPA filter. The low cost arrangement used mosquito netting as a pre-filter with a fiberglass furnace filter and an electrostatic furnace filter.
The commercially significant result is that the 95 percent DOP 0.3 micron filter matched HEPA at zero transmissions. HEPA works, and its cost and pressure penalty put it beyond most commercial sow farms, which is why it remains largely confined to boar studs. Demonstrating equivalent protection in this model from a filter without those penalties is what made barn scale filtration a practical proposition. The foundational work by Dee and colleagues in 2005 had already shown MERV 14 preventing transmission in a dual chamber model; this study established where the boundaries of adequate media sit.
The failures are the more useful half for a producer. Improvised low cost media let virus through in four of ten replicates, and bag filtration alone in two of ten. Neither is a cheaper route to the same outcome; both are a different outcome. Note also that the ten replicate arms make this a rank ordering under controlled challenge rather than a field failure rate. And the EU8 and EU13 designations belong to the European standards of that era, so they should be quoted with the scheme attached and never silently converted into a MERV number.