Evaluation of the risk for infection via three transmission routes using droplet deposition and tracer gas from a cough machine

The three routes of infectious disease transmission include airborne, contact, and droplet infection. It is necessary to evaluate the impact of each infection route under the same conditions, to more precisely determine infection risks. In the present study, we conducted a series of experiments to evaluate the integrated risk of infection through the various infection routes. In the droplet deposition experiment, the number of droplets deposited on membranes and environmental surfaces were measured using water-sensitive paper. The relative humidity (RH) was varied to assess its effect on droplets. In a droplet nuclei experiment, carbon dioxide gas was used as a tracer. On the basis of these results, the exposure impacts of each infection route were compared under the same RH conditions. The number of droplets deposited on eyes at 30% RH was about 20% lower than the number at 50% RH. The interrelationship between the various infection routes must be considered when developing programs to prevent infection.