Occupational exposures to transmissible agents is a recognized hazard which has received limited attention. Research into risk assessment and determinants of transmission of airborne pathogens has been a neglected area of study in general, and little is known about the nature of influenza virus transmission amongst humans in particular. Agricultural and healthcare workers are at high risk of influenza illness in the event of a pandemic due an influenza virus of swine or avian origin. This has been reflected in a recent NIOSH-issued alert addressing the risk for avian influenza in poultry workers (NIOSH Publication No. 2008-113), advising employers about pre- pandemic and pandemic measures. The purpose of this research is to determine the relative contributions of large respiratory droplets and small droplet nuclei to the spread of influenza viruses and to characterize the conditions under which transmission occurs. Using a novel mammalian model recently developed by our group for the study of human influenza virus transmission, we will use the guinea pig model for the study of the spread of influenza virus amongst mammals. We will characterize infectious particle distribution in exhaled breaths of influenza virus-infected guinea pigs using the NIOSH Cyclone air sampler. We will also determine the role of droplet nuclei in the spread of influenza viruses by conducting long-range transmission experiments and determine whether or not temperature and relative humidity impact airborne transmission of human influenza viruses. The guinea pig model will also be used to examine the presence and survival of avian H5N1 influenza virus in the air. We will identify host factors affecting airborne spread, more specifically, the impact of symptoms such as sneezing and host immune status upon transmission will be studied. These may represent risk factors for the spread of influenza virus in the workplace. Finally, the use of environmental and physical approaches such as ultraviolet irradiation and filtration of the air for the abrogation of influenza virus transmission will be investigated using this model. These findings will be central to the development of means to abrogate influenza virus transmission and improve safety in high risk work environments such as poultry farms and acute care health centers. RELEVANCE (See instructions): Identification of the determinants of transmission for influenza virus, a pathogen with pandemic potential, will allow for the development of effective control measures in the workplace and public spaces in general, thus improving safety and productivity. In addition, these measures may also be applicable to the control of the spread of other airborne pathogens.