Children exhale significantly fewer potentially infectious particles than adults—at least for the small droplets that are produced mainly in the lungs.
Key findings of a study conducted by the Max Planck Institute for Dynamics and Self-Organization (MPI-DS) and the Institute of Chemistry in collaboration with UMG. The researchers investigated the concentrations of aerosol particles and liquid droplets released with the breath when breathing, speaking, singing and shouting, taking measurements in 132 people of various ages. The findings help understand how to control the spread of diseases such as influenza or Covid-19.
Coronavirus disease
Infectious diseases are usually spread by particles exhaled by an infected person. However, the size of these aerosol particles varies widely, depending on its source in the respiratory tract. In the lungs, mostly small particles smaller than 5 microns -- or five thousandths of a millimeter -- are produced, also known as PM5. In contrast, larger particles are produced in the upper airways. The measurements showed that children exhaled far fewer small particles than adults.
"We found that the concentration of small particles below 5 micrometers increases with age, and that the concentration is especially low in children. Therefore, adults are more likely to trigger transmission if the infection is only in the lower respiratory tract," said the head of the MPI-DS research team, said Mohsen Bagheri, lead author of the study. Notably, larger particles from the throat spread to the same extent in children and adults, according to the study. The researchers found no correlation between the concentration of exhaled particles and a person's sex, weight, health status or smoking habits.
Vocal activity increases the concentration of small particles
In this comprehensive study, the researchers recorded data from 132 healthy volunteers. The study also included children and adolescents aged 5 to 18, for which data are scant. They used various instruments installed in the clean room to measure the full range of exhaled particle sizes: from one-tenth of a micron to one-quarter of a millimeter. Participants performed a total of 20 minutes of different vocal activities such as singing, speaking, and shouting. "Voice and age were shown to be independent risk factors for particle production," reports Professor Simone Scheithauer from the Department of Infection Control and Infectious Diseases at the University of Michigan.
Exhaled Particle Volume Determines Potential Infection Risk
While human droplets and aerosols mostly contain small particles, larger particles make up the majority of the total volume that can contain pathogens. Eberhard Bodenschatz, director of the MPI-DS, explains: "If the pathogen is mainly present in the upper respiratory tract, then large particles are by far the main vectors of disease. It is therefore important to consider the localization of infectious particles in the respiratory tract in order to decide on the appropriate Protective measures. For example, the current Omicron variant of the coronavirus seems to be more confined to the upper respiratory tract, which is why even a simple filter mask is a good protection."
new crown infection
Protection depends on pathogen localization
In contrast, infectious diseases that are mainly present in the lungs are mainly transmitted by small particles. Because their production increases with age, children are less likely than adults to transmit such diseases, according to the study. To prevent the airborne transmission of lung diseases, wearing a well-fitting, high-efficiency mask can effectively prevent the spread of the disease, especially for adults.
