Size Distributions of Influenza Virus Bioaerosols

Wan Yang (1), LINSEY C. MARR (1)

(1) Virginia Tech

     Abstract Number: 378
     Last modified: May 11, 2010

Abstract
Influenza viruses can be transmitted through direct contact, indirect contact involving fomites, large respiratory droplets, and droplet nuclei (aerosols) that are left behind by the evaporation of large droplets. The relative importance of each route remains contentious. To determine the potential for the flu to spread via the aerosol route, we have measured the size distribution of influenza viruses in fine particles. Using a cascade impactor, we collected a total of 16 samples during the 2009-2010 flu season in a health center, a daycare facility, and onboard three aircraft. Temperature and relative humidity (RH) were also recorded. Filter extracts were analyzed using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) targeting a gene segment of the influenza A virus. Eight samples were positive, and their virus concentrations ranged from 5800 to 37,000 genome copies per cubic meter. On average, over half of virus-laden particles were found on the two largest stages of the impactor: 1.0-2.5 and >2.5 micrometers. Because qRT-PCR simply measures all ribonucleic acid, whether the measured viruses were active or not is unknown. Virus concentrations were negatively correlated with relative and absolute humidity (RH and AH) for particles between 1.0-2.5 micrometers only. Modeling of virus concentrations indoors suggests a source strength of 140,000 +/- 100,000 genome copies per cubic meter per hour and a deposition flux onto surfaces of 6 +/- 4 genome copies per square meter per hour. Airborne influenza viruses are present as small enough particles to remain suspended for hours and to deposit to surfaces by Brownian motion.