PRRS has been found to be transported by fomites such as boots and containers, but it was not believed to be transferred with aerosols. This was proven wrong by tests done by Cho et al as they were able to observe a PRRS virus that traveled one mile by aerosol. Although this was difficult for other researchers to achieve or even repeat by the original team. It was found that a modified version of the virus was able to attach to particles such as dust and water to travel long distances. Hog farms in France were able to apply positive air pressure along with high efficiency filters to limit the movement of PRRS, but this was found to not be practical in the US due to different air pressure systems and the costs would not makes sense economically. So researchers set out to find a cheap alternative to this method applicable to US hog operations. A model was set up to replicate a dense pig population involving 300 head of middle aged pigs. Three barns were involved in the study, one was inoculated with PRRS, one was naive and had a high quality filter, and one was naive and held in a poorly filtered barn. Over a year air and blood samples were taken and analyzed for PRRS. Results showed that there was no sign of PRRS in the well filtered barn, and while no pigs became infected in the poorly ventilated barn, 10% of the air samples taken had evidence of PRRS. No hog operation since the onset of PRRS has been able to consistently produce weaned pigs who are PRRS negative. Air filtration is potentially one step towards sustainable PRRS negative production.