Inventing aerosols: Auguste Trillat (1861-1944) and the medical meteorology of influenza

This article explores Auguste Trillat’s pioneering research into the airborne transmission of influenza and the impact of meteorological factors on epidemics. A distinguished French chemist and microbiologist at the Institut Pasteur, Trillat was the first to demonstrate the airborne transmission of influenza. He applied the concept of aerosol in physics to epidemiology and updated miasma theory, which had become obsolete after Pasteur’s microbiology. Initially focused on formaldehyde chemistry, Trillat became increasingly interested in the airborne transmission of infectious diseases and methods for its control. His work on antisepsis drew inspiration from historical fumigation practices that uti lized formaldehyde as an effective antiseptic. Trillat’s experiments on air quality and pathogen growth in decaying environments revealed that factors such as humidity and temperature critically influenced the vitality and airborne trans mission of the pathogen. He highlighted the role of atmospheric conditions in epidemics and introduced the concept of “condensation nuclei,” in which micro bes act as droplet nuclei, aiding airborne transmission under certain atmospheric conditions. This model linked the spread of influenza to specific meteorological contexts. Trillat demonstrated that recently exhaled air, rich in moisture and nu tritive gases, promoted epidemic spread. His insights significantly advanced the fields of epidemiology and medical meteorology, gaining recognition for mili tary applications post-WWI in France and post-WWII worldwide, particularly in chemical and biological warfare. His findings on airborne pathogen transmission informed strategies for both offensive and defensive measures in military set tings, underscoring the importance of air quality control to mitigate the spread of infectious agents in hazardous environments.