Study: Exhaled COVID-19 Aerosol Droplets Dictated by Age, Infection and Body Mass Index

A recently published observational study in the Proceedings of the National Academy of Sciences suggests there is a strong positive association between the number of coronavirus disease 2019 (COVID-19) aerosol droplets an individual breathes out with age, infection and body weight.

In the study, a small team of researchers from Massachusetts and Louisiana measured general aerosol rates in 194 healthy participants. Additionally, the researchers examined how the progress of COVID-19 infection affected the quantity and size of aerosol droplets in 8 nonhuman primates (NHPs). The human group was comprised of 74 food workers as well as 120 students, staff and faculty from a community college.

During the study, human participants spent approximately 30 minutes per session breathing into a particle detector connected to standard nebulizer tubing. Researchers also collected biosamples from the NHPs infected with the novel coronavirus and measured the particle size and number exhaled by these primates using a modified pediatric face mask that was connected to a particle counter.

In the human study group, a total of 35 participants exhaled 80% of aerosols, which seemed to reflect the 20:80 superspreader rule of infection distribution. The investigators wrote that factors involved in altering droplet generation as well as the size of droplets during breathing include diet, aging and COVID-19 infection.

A total of 73 people with the lowest body mass index (BMI)-years, calculated as age multiplied by BMI, exhaled less aerosol droplets compared with 73 participants with the highest BMI-years.

In the NHP study group, the production of aerosol droplets appeared to follow the viral replication patterns for severe acute respiratory syndrome coronavirus 2. The aerosol production increased at Day 3 following infection and peaked at Day 7. This production subsequently declined rapidly by Day 14 and was undetectable by Day 27. Sizes of the aerosol droplets in NHPs were smallest when the infection was at its peak.

"These findings suggest that quantitative assessment and control of exhaled aerosol may be critical to slowing the airborne spread of COVID-19 in the absence of an effective and widely disseminated vaccine," wrote the researchers.

"While we are working toward a widely disseminated COVID-19 vaccine, this research shows the value in daily cleansing of our upper airways to reduce the spread of respiratory droplets emitted," said lead study author Dr. David Edwards of Harvard University, in a statement. "The role that airway hygiene plays in controlling the transmission and infection of COVID-19 and other respiratory infectious diseases including Tuberculosis and Influenza, is becoming clearer."

The new research coincides with recently published research from the Centers for Disease Control and Prevention (CDC), which state that double-masking, compared with wearing a single mask, cuts COVID-19 droplet exposure by more than 95%. As such, the CDC now recommends the public wear two masks instead of one, advocating for the use of an N95 with a cloth or surgical mask.

“In light of the new COVID-19 variants which are estimated to be at least 50% more transmissible, it is imperative that we must be more vigilant than ever,” said Dr. Andrea Love, immunologist, microbiologist and co-host of a weekly podcast called Unbiased Science, in a previously published interview on BioSpace. “With a more transmissible virus, that means every exposure has increased likelihood of leading to spread. We must be more stringent with our behaviors now, including social distancing, minimizing trips to public places, avoiding indoor spaces, and ALWAYS wear a mask. But, not just any mask will do – quality matters.”