Children exhale far fewer potentially infectious particles than adults – at least that’s true for small respiratory droplets that are primarily produced in the lungs. This is a key finding of a study conducted by the Max Planck Institutes for Dynamics and Self-Organization (MPI-DS) and for Chemistry in collaboration with the University of Göttingen Medical Center ( UMG). The researchers studied the concentrations of aerosol particles and droplets emitted with respiration during breathing, speaking, singing and shouting, using measurements on 132 people of all ages. The results help to understand how the spread of diseases like influenza or Covid-19 can be contained.
Infectious diseases are often transmitted by particles exhaled by infected people. However, the size of these aerosol particles varies greatly according to their origin in the respiratory tract. In the lungs, most of the time, small particles of less than five microns – ie five thousandths of a millimeter – are produced, also called PM5. In contrast, larger particles are produced in the upper respiratory tract. As measurements have shown, children exhale significantly fewer smaller particles than adults. “We found that the concentration of small particles below five microns 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,” says Mohsen Bagheri, research group leader and lead study author at MPI-DS. Notably, larger particles that come from the throat are spread by children and adults to the same extent, according to the study. The researchers did not find a correlation between the concentration of exhaled particles and a person’s gender, weight, physical condition or smoking habits.
Vocalization activities increase the concentration of small particles
In this extensive study, researchers recorded data from 132 healthy volunteers. The study also included children and adolescents between the ages of 5 and 18 for whom very little data was available. They used various instruments set up in a clean room to measure the full range of exhaled particle sizes: from tenths of a micrometer to a quarter of a millimeter. Participants performed different vocalization activities such as singing, talking, and shouting for a total of 20 minutes. “Vocalization and age appear to be independent risk factors for particle production,” reports Professor Simone Scheithauer from the Department of Infection Control and Infectious Diseases at UMG.
The volume of exhaled particles determines the potential risk of infection
Although human drops and aerosols contain mostly small particles, larger particles make up most of the total volume that can contain pathogens. “While the pathogen primarily resides in the upper respiratory tract, large particles are by far the main vector of the disease,” explains Eberhard Bodenschatz, director at MPI-DS. “It is therefore important to consider the location of the infectious particle in the respiratory tract to decide on appropriate protection,” he continues. “For example, the current Omicron variant of the Coronavirus seems to be localized more in the upper respiratory tract and that is why even simple filtering masks are excellent protection.”
Protective measures depend on the location of the pathogen
In contrast, infectious diseases that reside primarily in the lungs will be primarily transmitted via small particles. Since their production increases with age, children are less likely to transmit such diseases than adults, according to the study. To prevent airborne transmission of lung disease, wearing well-fitting, high-efficiency face masks can therefore be an effective measure to prevent disease transmission, especially for adults.
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