Risk assessment for airborne disease transmission by poly-pathogen aerosols

TL;DR

This paper extends the Wells-Riley model to account for poly-pathogen aerosols, providing a more accurate risk assessment for airborne disease transmission, especially at high pathogen concentrations and in poorly ventilated environments.

Contribution

It introduces a generalized model that separately considers multiple pathogen copies per aerosol, improving upon the traditional mono-pathogen assumption.

Findings

Mono-pathogen assumption overestimates infection risk at high pathogen loads.

The model accounts for aerosol filtering and facemask effects.

Risk assessment accuracy improves in high-density, poorly ventilated settings.

Abstract

In the case of airborne diseases, pathogen copies are transmitted by droplets of respiratory tract fluid that are exhaled by the infectious and, after partial or full drying, inhaled as aerosols by the susceptible. The risk of infection in indoor environments is typically modelled using the Wells-Riley model or a Wells-Riley-like formulation, usually assuming the pathogen dose follows a Poisson distribution (mono-pathogen assumption). Aerosols that hold more than one pathogen copy, i.e. poly-pathogen aerosols, break this assumption even if the aerosol dose itself follows a Poisson distribution. For the largest aerosols where the number of pathogen in each aerosol can sometimes be several hundred or several thousand, the effect is non-negligible, especially in diseases where the risk of infection per pathogen is high. Here we report on a generalization of the Wells-Riley model and dose-response models for poly-pathogen aerosols by separately modeling each number of pathogen copies per aerosol, while the aerosol dose itself follows a Poisson distribution. This results in a model for computational risk assessment suitable for mono-/poly-pathogen aerosols. We show that the mono-pathogen assumption significantly overestimates the risk of infection for high pathogen concentrations in the respiratory tract fluid. The model also includes the aerosol removal due to filtering by the individuals which becomes significant for poorly ventilated environments with a high density of individuals, and systematically includes the effects of facemasks in the infectious aerosol source and sink terms and dose calculations.