Air sampling carried out during active outbreaks on working swine and poultry premises detected PEDV, highly pathogenic avian influenza H5N2, and PRRSV in aerosolized particles. PEDV and HPAIV both showed bimodal particle size distributions. PRRSV appeared at low frequency, in 8 percent of sampling events. For all three viruses, higher RNA copy numbers were associated with the larger particles, and the sampling floor was 0.4 micron.
This is the field companion to the 2015 chamber study by Alonso, Raynor, Davies and Torremorell, which sampled aerosols from experimentally infected pigs under controlled conditions. The 2017 work carries the same question into barns during real outbreaks, and its H5N2 data come from the 2015 US Midwest HPAI outbreak on turkey and layer premises in Minnesota, Iowa and Nebraska. It stands as the first published field measurement of HPAIV carrier size distribution, which gives the poultry side of the carrier particle question its first field entry. Alonso 2013 sits behind both papers as the epidemiological case for filtration in swine dense regions.
One limitation governs how this study can be used. Detection was by RNA, and infectivity was not tested by size fraction, so the results describe where viral genetic material was found rather than where viable virus was recovered. That distinction matters because the 2.1 micron figure circulating in this literature is a stage cut point on an Andersen cascade impactor, an instrument bin edge and not a biological boundary. For design work the usable finding is directional: in outbreak conditions, virus laden material is distributed across a wide range of particle sizes, with the greater share of genetic material carried on coarser particles.