Laboratory Study on Sampling and Detection of Airborne Influenza Virus

GANG CAO (1), Francoise M. Blachere (1), William G. Lindsley (1), Bean T Chen (1), Donald H. Beezhold(1)

(1) NIOSH, Morgantown, WV

     Abstract Number: 214
     Last modified: April 29, 2010

Abstract
There is considerable debate over whether aerosols play a significant role in the transmission of influenza. Better methods for sampling and detection of viable airborne influenza virus are greatly needed. We evaluated the performance of two types of bioaerosol samplers for collecting airborne influenza under controlled laboratory conditions. Experiments were conducted in a calm-air chamber at 20% humidity and at room temperature. A diluted influenza viral solution [A/WS/33 (H1N1)] was aerosolized (AeroNeb) into the chamber and collected with both NIOSH samplers and SKC BioSamplers. Viability and total viral particle counts were determined by viral plaque assay (VPA) and quantitative polymerase chain reaction (qPCR), respectively. Preliminary results showed that, only small amounts of viable virus (0.1-2%) could be detected in the aerosol using VPA. Compared with SKC BioSamplers, NIOSH samplers collected a similar amount of total viral particles but had a 49% decline in viral viability. Results indicated that the VPA was not sensitive enough to evaluate the viability of airborne influenza virus. A modified TCID50 assay (VRA) using qPCR was found to be 1000-fold more sensitive than the VPA and demonstrated high viral loads in extracts from both the NIOSH samplers (4.3E+10 copies/mL) and SKC BioSamplers (2.4E+11 copies/mL) when assayed 24 hours post-inoculation. An advantage of the NIOSH sampler is that it enables a detailed analysis of particle size distributions. At a 3.5 L/min, the NIOSH sampler size-fractionates and collects particles with an aerodynamic diameter (da) > 4 µm in stage 1, da = 1-4 µm in stage 2, and da < 1 µm on the back-up filter. Results using VPA showed that the majority of viable influenza particles (88%) were contained in aerosols with da < 4 µm. This data suggests that small respirable particles can contain viable virus and may play a role in viral transmission.