The SARS-CoV-2 virus is transmitted through aerosols that are generated when an infected person breathes, talks, sneezes, or coughs. The amount and size of aerosol droplets a person exhales can vary drastically between individuals and may be affected by diet and age. Findings of a recent study suggest that humans and non-human primates with greater age and body mass index (BMI) produce more aerosol droplets during COVID-19 infection.

Aerosol droplets are produced when air passes over mucus-coated airways during breathing. This mucus determines the size of aerosol droplets produced. A healthy mucus layer forms large droplets, while a dysfunctional mucus layer produces droplets that aerosolize into many smaller infectious droplets. Mucus structure and composition are influenced by age, environment, disease, and the microbiota. A Western, obesity-promoting diet is often deficient in fiber, starving the beneficial bacteria in the gut that produce metabolites such as short chain fatty acids that regulate the lung mucus barrier. Older adults also experience degradation of the lung mucus layer, potentially influencing aerosol droplet size.

The researchers recruited 194 participants from the United States. They asked participants to breathe into a particle detector to measure the quantity of exhaled particles in the size range of three to five micrometers. They characterized participants who exhaled 156 particles per liter of air or less during the breath test as low spreaders and participants above this level of superspreaders. The particle detector was connected to an air filter that collected the particles so the concentration of SARS-CoV-2 virus could be measured. The investigators also used a sample of eight non-human primates to better understand the effects of SARS-CoV-2 infection. The investigators exposed rhesus macaques and green monkeys to either the SARS-CoV-2 or tuberculosis virus and monitored them for up to 60 days. The non-human primates performed a similar breath test as the one used in the human participants.

The authors found no relationship between sex and aerosol particle number; however, there were significant statistical relationships among age, BMI, and particle size. The strongest correlation was found between particle size and BMI-years, which is calculated as BMI multiplied by age. Participants in the bottom 50 percent for BMI-years exhaled significantly less aerosol than participants in the top 50 percent. In non-human primates, SARS-CoV-2 or tuberculosis infection increased the number of aerosol particles exhaled in proportion to the amount of viral RNA measured from mucus swabs.

The authors concluded that age, BMI, and active infection decrease aerosol particle size and may contribute to viral spread. Future models of pandemic progression should take these factors into account.

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