Particle sizes of infectious aerosols: implications for infection control

Abstract

The global pandemic of COVID-19 has been associated with infections and deaths among health-care workers. This Viewpoint of infectious aerosols is intended to inform appropriate infection control measures to protect health-care workers. Studies of cough aerosols and of exhaled breath from patients with various respiratory infections have shown striking similarities in aerosol size distributions, with a predominance of pathogens in small particles (<5 μm). These are immediately respirable, suggesting the need for personal respiratory protection (respirators) for individuals in close proximity to patients with potentially virulent pathogens. There is no evidence that some pathogens are carried only in large droplets. Surgical masks might offer some respiratory protection from inhalation of infectious aerosols, but not as much as respirators. However, surgical masks worn by patients reduce exposures to infectious aerosols to health-care workers and other individuals. The variability of infectious aerosol production, with some so-called super-emitters producing much higher amounts of infectious aerosol than most, might help to explain the epidemiology of super-spreading. Airborne infection control measures are indicated for potentially lethal respiratory pathogens such as severe acute respiratory syndrome coronavirus 2.

Figure 1

Particle size distributions of cough aerosols from (A) patients with tuberculosis and (B) patients with cystic fibrosis infected with Pseudomonas aeruginosa (A) Reproduced from Fennelly et al, by permission of the American Thoracic Society. (B) Reproduced from Wainwright et al. Error bars represent 95% CIs. CFU=colony forming units.

Figure 2

Log-normal distributions of the magnitudes of cough aerosols from patients with influenza using (A) an Andersen cascade impactor and (B) a NIOSH two-stage aerosol sampler, coherent with super-spreading (A) Reproduced from Bischoff et al, by permission of Oxford University Press. (B) Reproduced from Lindsley et al. NIOSH=US National Institute of Occupational Safety and Health. HID₅₀=50% human infectious dose.

Figure 3

Proportions of influenza aerosol particles sizes in cough and exhaled breath sample collections Data extracted from primary references, for comparison. Influenza virus in exhaled breath is emitted in smaller particles than influenza virus in cough aerosols.