THE ESSENTIAL
- According to the study, breathing mainly produces small particles while vocalizations (speaking or singing) mainly produce large particles.
- Gender, BMI, smoking, or exercise habits have no discernible effect on PM5 concentration.
- Particles with a diameter of 15 µm from the mouth.
We became aware of this with the arrival of SARS-CoV-2 in our lives: we project microdroplets every time we speak or breathe. These contain infectious particles. The largest (> 5 microns) come from the upper respiratory tract, i.e. the mouth, nose, throat, larynx and trachea. The smallest (< 5 microns) emanate mainly from the lungs. A German study reveals that children are less likely to transmit it.
Children release fewer small infectious particles
The researchers brought together 132 volunteers. Among them were children and adolescents from 5 to 18 years old as well as adults (up to 80 years old). They asked all participants to sing, talk, shout, breathe deeply or even cough for 20 minutes. Instruments were used to measure the concentration of exhaled droplets as well as their size.
“Vocalizations and age appear to be independent risk factors for the production of infectious particles”reports Professor Simone Scheithauer from the Department of Infection Control and Infectious Diseases at the University of Göttingen.
Son collègue du Max Planck Institute for Dynamics and Self-Organization (MPI-DS), Mohsen Bagheri, ajoute : “We found that the concentration of small particles below five microns (PM5) increases with age and is particularly low in children. As a result, adults are much more likely to trigger the spread if the infection is only in the lower respiratory tract (the lungs, Editor’s note)”.
For a given activity and duration, the cumulative volume of PM5 emissions by the youngest is on average 6 to 8 times lower than that of the oldest. Larger particles that come from the throat are spread by children and adults to the same extent, according to the work presented.
Where exhaled particles come from determines the risk of infection
The study, published in the February 2023 edition of Journal of Aerosol Scienceshows that the location of germs in the respiratory tract plays an important role in the spread of infections.
“If the pathogen resides primarily in the upper respiratory tract, large particles are by far the main vector of disease”, explains Eberhard Bodenschatz, director of the MPI-DS. If the viruses are installed in the lungs, transmission is likely to occur mainly via small exhaled particles. Since their production increases with age, children are less likely to transmit pulmonary pathologies than adults.
Adults are “much more likely to trigger super-diffusion events in such a scenario”confirms the article. “To prevent airborne transmission of lung disease, wearing well-fitting, high-efficiency face masks may therefore be an effective measure to prevent disease transmission, especially for adults”conclude the researchers.