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.

Bioaerosol production by patients with tuberculosis during normal tidal breathing: implications for transmission risk

“…Group 1 was recruited during the previous study measuring bioaerosol production by healthy volunteers 5. Groups 2–4 were recruited from University College London NHS Foundation Trust (UCLH) TB service.…”

“…We have already shown the feasibility of measuring bioaerosols in healthy volunteers using optical particle counter (OPC) technology that measures the size and concentration of particles in exhaled breath during normal tidal breathing 5. This study makes an important next step by piloting OPC technology in patients with intrathoracic, extrathoracic and latent TB compared with healthy controls.…”

“…Based on our previous work showing that the first reading within a measurement session was poorly correlated with second and third readings in the session, we excluded the first reading from subsequent analyses 5. All analyses were performed using STATA V.13.0, IC (College Station, Texas, USA).…”

Modeling aerial transmission of pathogens (including the SARS-CoV-2 virus) through aerosol emissions from e-cigarettes

“…We have also considered simply droplet emission, disregarding the specification of a specific pathogen. Evidently, this oversimplification disregards important known facts, for example: droplet characteristics vary among pathogens and between healthy and infected subjects Fabian et al (2011); Wurie et al (2013).…”

“…While some of the studies in Table 2 were motivated by investigating droplet emission in the context of airborne pathogen contagion (for example Papineni and Rosenthal (1997); Fabian et al (2011); Wurie et al (2013); Asadi et al (2019)), the motivation of others is to probe various mechanisms of droplet formation (Johnson and Morawska (2009); Morawska et al (2009); Almstrand et al (2010); Holmgren et al (2010); Schwarz et al (2010, 2015), see comprehensive discussion and reviews in Wei and Li (2016); Bake et al (2019); Haslbeck et al (2010)), specifically the airway reopening hypothesis of small peripheral airways that normally close following a deep expiration, which was further tested by computerized modeling by Haslbeck et al (2010) who simulated this mechanism of particle formation by rupture of surfactant films involving surface tension. The mechanism was probed by Johnson and Morawska (2009) by showing that concentrations of exhaled particles significantly increase with breathing intensities higher than rest tidal volume, but also for fast exhalations but not fast inhalation, while droplet numbers increased up to two orders of magnitude: from ∼ 230/LT in tidal volume (0.7 Lt) to over 1200/LT in a breathing maneuver from fractional residual capacity to total lung capacity (see Almstrand et al (2010)).…”