Comparison of two size-differentiating air samplers for detecting airborne swine viruses under experimental conditions

Detection and quantification of dilute viral aerosols, as encountered outside animal housing facilities, requires methods that are able to detect small numbers of viruses in large volumes of air. This study compared the performance of two size-differentiating cascade impactors; an Andersen 8-stage ( ACI; 28.3 L/min) and a high volume Tisch ( TCI; 1,133 L/min) to assess sampling efficiency for detecting porcine reproductive and respiratory syndrome virus ( PRRSV) and influenza A virus ( IAV). Samples of particles sorted by aerodynamic diameter were analyzed by quantitative polymerase chain reaction ( qPCR) and collection efficiency was assessed by particle size. Collection media ( minimum essential medium [ MEM] and beef extract [ BE]), elution technique ( active versus passive), and sampling times ( 10, 20, and 30 min) were variables assessed for the TCI sampler. Extraction efficiency was 35% higher with BE as compared to that of MEM ( p = 0.0007); active extraction technique was 19% more efficient than the passive technique ( p = 0.03); time of sampling did not significantly affect the amount of virus recovered. The ACI sampler was more efficient in detecting both viruses from small and medium sized airborne particles ( <= 3 mm) as compared to the TCI sampler ( p < 0.001). The latter sampler, however, was more efficient at IAV detection from large airborne particles (> 3 mu m) ( p = 0.0025) indicating the potential of this sampler in detecting the presence of small amounts of viruses in aerosols under field conditions.