A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities. Distinct physiological processes were responsible for specific size distribution modes. The majority of particles for all activities were produced in one or more modes, with diameters below 0.8 m at average concentrations up to 0.75 cm −3 . These particles occurred at varying concentrations, during all respiratory activities, including normal breathing. A second mode at 1.8 m was produced during all activities, but at lower concentrations of up to 0.14 cm −3 . Speech produced additional particles in modes near 3.5 and 5 m. These two modes became most pronounced during sustained vocalization, producing average concentrations of 0.04 and 0.16 cm −3 , respectively, suggesting that the aerosolization of secretions lubricating the vocal chords is a major source of droplets in terms of number. For the entire size range examined of 0.3-20 m, average particle number concentrations produced during exhalation ranged from 0.1 cm −3 for breathing to 1.1 cm −3 for sustained vocalization. Non-equilibrium droplet evaporation was not detectable for particles between 0.5 and 20 m, implying that evaporation to the equilibrium droplet size occurred within 0.8 s.

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Size distributions of expiratory droplets expelled during coughing and speaking and the velocities of the expiration air jets of healthy volunteers were measured. Droplet size was measured using the interferometric Mie imaging (IMI) technique while the particle image velocimetry (PIV) technique was used for measuring air velocity. These techniques allowed measurements in close proximity to the mouth and avoided air sampling losses. The average expiration air velocity was 11.7 m/s for coughing and 3.9 m/s for speaking. Under the experimental setting, evaporation and condensation effects had negligible impact on the measured droplet size. The geometric mean diameter of droplets from coughing was 13.5 m and it was 16.0 m for speaking (counting 1-100). The estimated total number of droplets expelled ranged from 947 to 2085 per cough and 112-6720 for speaking. The estimated droplet concentrations for coughing ranged from 2.4 to 5.2 cm −3 per cough and 0.004-0.223 cm −3 for speaking.

Lung infections with Mycobacterium abscessus, a species of multidrug resistant nontuberculous mycobacteria, are emerging as an important global threat to individuals with cystic fibrosis (CF) where they accelerate inflammatory lung damage leading to increased morbidity and mortality. Previously, M. abscessus was thought to be independently acquired by susceptible individuals from the environment. However, using whole genome analysis of a global collection of clinical isolates, we show that the majority of M. abscessus infections are acquired through transmission, potentially via fomites and aerosols, of recently emerged dominant circulating clones that have spread globally. We demonstrate that these clones are associated with worse clinical outcomes, show increased virulence in cell-based and mouse infection models, and thus represent an urgent international infection challenge.Nontuberculous mycobacteria (NTM; referring to mycobacterial species other than M. tuberculosis complex and M. leprae) are ubiquitous environmental organisms that can cause chronic pulmonary infections in susceptible individuals [1,2], particularly those with preexisting inflammatory lung diseases such as cystic fibrosis (CF) [3]. The major NTM infecting CF individuals around the world is Mycobacterium abscessus; a rapidly growing, intrinsically multidrug-resistant species, which can be impossible to treat despite prolonged combination antibiotic therapy [1,[3][4][5], leads to accelerated decline in lung function [6,7], and remains a contraindication to lung transplantation in many centers [3,8,9].Until recently, NTM infections were thought to be independently acquired by individuals through exposure to soil or water [10][11][12]. As expected, previous analyses from the 1990s and 2000s [13][14][15][16] showed that CF patients were infected with unique, genetically diverse strains of M. abscessus, presumably from environmental sources. We used whole genome sequencing at a single UK CF center and identified two clusters of patients (11 individuals in total) infected with identical or near-identical M. abscessus isolates, which social network analysis suggested were acquired within hospital via indirect transmission between patients Phylogenetic analysis of these sequences (using one isolate per patient), supplemented by published genomes from US, France, Brazil, Malaysia, China, and South Korea (Table S1), was performed and analysed in the context of the geographical provenance of isolates ( Figure 1; Figure S1). Within each subspecies, we found multiple examples of deep branches (indicating large genetic differences) between isolates from different individuals, consistent with independent acquisition of unrelated environmental bacteria. However, we also identified multiple clades of near-identical isolates from geographically diverse locations (Figure 1), suggesting widespread transmission of circulating clones within the global CF patient community.To investigate further the relatedness of isolates from different individuals, we a...

Abstract:Background: Aerosol production during normal breathing is often attributed to