Respiratory Aerosol Measurements from Large Cohorts and a Longitudinal Study

JONATHAN P. REID, Bryan R. Bzdek, Nan Zhou, Andrew Shrimpton, Tony Pickering, University of Bristol

     Abstract Number: 37
     Working Group: Bioaerosols

Abstract
The amount of exhaled aerosol by respiratory and vocal activities and the concentration of carbon dioxide are often used to assess the risk of indoor transmission of respiratory pathogens by inhalation in the absence of quantitative information on airborne infectious and viable pathogen concentration. Measurements of exhaled aerosols present considerable and unique challenges that must be overcome when measuring exhaled aerosols. For example, the number of particles exhaled is extremely low and cannot be discriminated from the ambient particles in an indoor environment.

We will report on two large campaigns collecting data on respiratory aerosol and respiratory parameters (e.g. minute ventilation, forced vital capacity) from 400 participants and a longitudinal study to investigate how exhaled aerosols from an individual change over time. Distinctively, our studies have quantified the absolute amount of aerosol generated by a range of respiratory and vocal activities, including speech and language therapy, the correlation between particle emission rates and the amount of carbon dioxide exhaled, and the impact of pre-existing lung conditions and infection on emission.

We show that although carbon dioxide is a good measure of indoor ventilation, it is a poor indicator of the amount of aerosol exhaled. Indeed, vocalization can lead to 1-3 orders of magnitude more aerosol than breathing for no change in exhaled carbon dioxide. We will also show that there is no correlation between exhaled aerosol, participant age and body mass index, and that the aerosol number concentrations emitted by those with pre-existing lung conditions and healthy subjects are similar.

From our longitudinal study, we will report measurements of exhaled aerosols over day, week and month timescales. This study is being used to examine the importance of physiological factors in determining exhaled aerosol and to answer the question: are individuals who are high emitters of aerosol particles always high emitters?