Dynamics of Infectious Disease Transmission by Respirable Droplets

Transmission of respiratory infectious diseases in humans, for instance influenza, occurs by several modes. Respirable droplets, droplets whose pre-evaporation aerodynamic diameter is less than 20 microns, provide a vector of transmission of an infectious pathogen that may contribute to different transmission modes. Larger droplets either evaporate very fast or gravitationally settle, their effect being rather limited except for very close contacts between susceptible and infected persons. An epidemiological model with explicit consideration of the dynamics of respirable droplets is developed to assess their relevance in the infectious process. Respirable droplets are divided into three classes: fine, coarse and settled. Droplet dynamics is determined by their physical properties (size), whereas the population dynamics by the infectivity of the pathogen. The size and number of droplets shed by an infected person via expulsion events (e.g. sneezing, coughing, talking) are important physical parameters as they determine the residence time a droplet remains airborne, its regional deposition in the respiratory tract, and the amount of pathogen carried. We argue, using estimates from experimental studies, that respirable droplets are a dynamically possible transmission vector for influenza. Airborne coarse droplets may provide the dominant transmission mode, the relative importance of transmission modes depending on model parameters. The impact of settled pathogen-carrying droplets depends on the inactivation rates of the pathogen in different environmental media. The model provides an expandable theoretical framework, which in combination with better experimental data, could contribute to understanding the transmission of respiratory infectious diseases, to evaluate the effects of associated control strategies, and to assess the relative importance of transmission modes.

STILIANAKIS Nikolaos;  DROSSINOS Ioannis; 

2008-11-24

European Centre for Disease Prevention and Control (ECDC)

JRC47464

https://publications.jrc.ec.europa.eu/repository/handle/JRC47464,