title: Characteristics of exhaled particle production in healthy volunteers: possible implications for infectious disease transmission.
abstract: The size and concentration of exhaled particles may influence respiratory infection transmission risk. We assessed variation in exhaled particle production between individuals, factors associated with high production and stability over time. We measured exhaled particle production during tidal breathing in a sample of 79 healthy volunteers, using optical particle counter technology. Repeat measurements (several months after baseline) were obtained for 37 of the 79 participants.   Multilevel linear regression models of log transformed particle production measures were used to assess risk factors for high production.  Stability between measurements over time was assessed using Lin's correlation coefficients. Ninety-nine percent of expired particles were <1μm in diameter. Considerable variation in exhaled particle production was observed between individuals and within individuals over time. Distribution of particle production was right skewed.  Approximately 90% of individuals produce <150 particles per litre in normal breathing.  A few individuals had measurements of over 1000 particles per litre (maximum 1456). Particle production increased with age (p<0.001) and was associated with high tree pollen counts. Particle production levels did not remain stable over time [rho 0.14 (95%CI -0.10, 0.38, p=0.238)]. Sub-micron particles conducive to airborne rather than droplet transmission form the great majority of exhaled particles in tidal breathing. There is a high level of variability between subjects but measurements are not stable over time. Production increases with age and may be influenced by airway inflammation caused by environmental irritants. Further research is needed to determine whether the observed variations in exhaled particle production affect transmission of respiratory infection.
authors.affiliation: Centre of Infectious Disease Epidemiology, Research Department of Infection and Population Health, University College London, London, UK.
authors.forename: Fatima
authors.initials: F
authors.lastname: Wurie
authors.affiliation: Centre of Infectious Disease Epidemiology, Research Department of Infection and Population Health, University College London, London, UK.
authors.forename: Olivier
authors.initials: O
authors.lastname: Le Polain de Waroux
authors.affiliation: Pulmatrix Inc., Lexington, 02421, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Brande
authors.affiliation: Pulmatrix Inc., Lexington, 02421, USA.
authors.forename: Wesley
authors.initials: W
authors.lastname: Dehaan
authors.affiliation: Centre of Infectious Disease Epidemiology, Research Department of Infection and Population Health, University College London, London, UK.
authors.forename: Katherine
authors.initials: K
authors.lastname: Holdgate
authors.affiliation: Centre of Infectious Disease Epidemiology, Research Department of Infection and Population Health, University College London, London, UK.
authors.forename: Rishi
authors.initials: R
authors.lastname: Mannan
authors.affiliation: Maryland Institute of Applied Environmental Health, University of Maryland School of Public Health, College Park, 20742, USA.
authors.forename: Donald
authors.initials: D
authors.lastname: Milton
authors.affiliation: Research Department of Epidemiology and Public Health, University College London, London, WC1E 6BT, UK.
authors.forename: Daniel
authors.initials: D
authors.lastname: Swerdlow
authors.affiliation: Centre of Infectious Disease Epidemiology, Research Department of Infection and Population Health, University College London, London, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Hayward