Researchers were able to determine that the PRRS virus transfers between pigs by way of aerosol. It was also determined that the more virulent the disease was the higher chances it has of shedding and infecting other pigs. Identifying these factors has led to a need to develop an air filtration system capable of stopping the PRRS virus from traveling from an infected herd to a non-infected herd. A filtration system put in place by French hog farmers was able to eliminate PRRS outbreaks in an area that was once commonly infected with the virus. This method involved three filters one being high efficiency particulate air (HEPA) filter capable of filtering particles as small as 0.3 microns. To prove the effectiveness of this method American researchers ran a series of  tests involving PRRS infected pigs. The PRRS infected pig was put in one room and a PRRS negative pig was put in a room beside it with the filter placed between them. In 20 trials the PRRS negative pig was not infected with the virus, when the same test was done without the filter the negative pig was infected 6 out of 20 times. To intesify the study the researchers used 2 pints of solution containing PRRS to create a “virus fog” which was put through the filter. When the filter was in place for 10 trails the negative pig was not infected once, where as in the control when the filter was removed the negative pig was infected 9 out of 10 times. This HEPA filter was put in place in a  barn in Iowa that consistently suffered from PRRS outbreaks annually between November and February. After a year of having the filter in place the barn suffered no out breaks and the staff veterinarian said that the overall environment of the barn had been improved.