Airborne Transmission of Influenza a Virus in Indoor Environments

Yang, Wan

Airborne Transmission of Influenza a Virus in Indoor Environments

dc.contributor.author	Yang, Wan	en
dc.contributor.committeechair	Marr, Linsey C.	en
dc.contributor.committeemember	Little, John C.	en
dc.contributor.committeemember	Subbiah, Elankumaran	en
dc.contributor.committeemember	Pruden, Amy	en
dc.contributor.department	Civil Engineering	en
dc.date.accessioned	2017-04-06T15:45:03Z	en
dc.date.adate	2012-04-26	en
dc.date.available	2017-04-06T15:45:03Z	en
dc.date.issued	2012-03-30	en
dc.date.rdate	2016-10-24	en
dc.date.sdate	2012-04-01	en
dc.description.abstract	Despite formidable advances in virology and medicine in recent decades, we know remarkably little about the dynamics of the influenza virus in the environment during transmission between hosts. There is still controversy over the relative importance of various transmission routes, and the seasonality of influenza remains unexplained. This work focuses on developing new knowledge about influenza transmission via the airborne route and the virus' inter-host dynamics in droplets and aerosols. We measured airborne concentrations of influenza A viruses (IAVs) and size distributions of their carrier aerosols in a health center, a daycare center, and airplanes. Results indicate that the majority of viruses are associated with aerosols smaller than 2.5 µm and that concentrations are sufficient to induce infection. We further modeled the fate and transport of IAV-laden droplets expelled from a cough into a room, as a function of relative humidity (RH) and droplet size. The model shows that airborne concentrations of infectious IAV vary with RH through its influence on virus inactivation and droplet size, which shrinks due to evaporation. IAVs associated with large droplets are removed mostly by settling, while those associated with aerosols smaller than 5 µm are removed mainly by ventilation and inactivation. To investigate the relationship between RH and influenza transmission further, we measured the viability of IAV in droplets at varying RHs. Results suggest that there exist three regimes defined by RH: physiological conditions (~100% RH) with high viability, concentrated conditions (~50% to ~99% RH) with lower viability, and dry conditions (<~50% RH) with high viability. A droplet's extent of evaporation, which is determined by RH, affects solute concentrations in the droplet, and these appear to influence viability. This research considerably advances the current understanding of the dynamics of the influenza virus while it is airborne and provides an explanation for influenza's seasonality. Increased influenza activity in winter in temperate regions could be due to greater potential for IAV carrier aerosols to remain airborne and higher viability of IAV at low RH. In tropical regions, transmission could be enhanced due to better survival of IAV at extremely high RH.	en
dc.description.degree	Ph. D.	en
dc.identifier.other	etd-04012012-212415	en
dc.identifier.sourceurl	http://scholar.lib.vt.edu/theses/available/etd-04012012-212415/	en
dc.identifier.uri	http://hdl.handle.net/10919/77340	en
dc.language.iso	en_US	en
dc.publisher	Virginia Tech	en
dc.rights	In Copyright	en
dc.rights.uri	http://rightsstatements.org/vocab/InC/1.0/	en
dc.subject	influenza A virus	en
dc.subject	airborne transmission	en
dc.subject	relative humidity	en
dc.subject	size distribution	en
dc.subject	bioaerosol	en
dc.title	Airborne Transmission of Influenza a Virus in Indoor Environments	en
dc.type	Dissertation	en
dc.type.dcmitype	Text	en
thesis.degree.discipline	Civil Engineering	en
thesis.degree.grantor	Virginia Polytechnic Institute and State University	en
thesis.degree.level	doctoral	en
thesis.degree.name	Ph. D.	en