The Size Distribution of Droplets in the Exhaled Breath of Healthy Human Subjects

TLDR

Droplets in exhaled breath can carry microorganisms, and their size distribution determines which organisms are transmitted and informs airborne infection control strategies. This study aimed to characterize the size distribution of droplets exhaled by healthy individuals. Researchers measured exhaled droplets from subjects performing mouth breathing, nose breathing, coughing, and talking using an optical particle counter and an analytical transmission electron microscope. Most particles were smaller than 1 µm, yet larger droplets were also detected; coughing produced the highest droplet concentrations, nose breathing the lowest, with substantial inter‑subject variability.

Abstract

Droplets carried in exhaled breath may carry microorganisms capable of transmitting disease over both short and long distances. The size distribution of such droplets will influence the type of organisms that may be carried as well as strategies for controlling airborne infection. The aim of this study was to characterize the size distribution of droplets exhaled by healthy individuals. Exhaled droplets from human subjects performing four respiratory actions (mouth breathing, nose breathing, coughing, talking) were measured by both an optical particle counter (OPC) and an analytical transmission electron microscope (AEM). The OPC indicated a preponderance of particles less than 1 mu, although larger particles were also found. Measurements with the AEM confirmed the existence of larger sized droplets in the exhaled breath. In general, coughing produced the largest droplet concentrations and nose breathing the least, although considerable intersubject variability was observed.