Quantitative microbial risk assessment of contracting COVID-19 derived from measured and simulated aerosol particle transmission in aircraft cabins

Abstract

Background SARS-CoV-2 can be effectively transmitted between individuals located in close proximity to each other for extended durations. Aircraft provide such conditions. Although high attack rates during flights were reported, little was known about the risk levels of aerosol transmission of SARS-CoV-2 in aircraft cabins.

Objectives The major objective was to assess the risk of contracting COVID-19 from exposure to SARS-CoV-2-containing aerosol particles in aircraft cabins.

Methods In two single-aisle and one twin-aisle aircraft, dispersion of generated aerosol particles over a 7-row economy-class cabin section was measured under cruise and taxi conditions and simulated with a CFD model under cruise conditions. Using the aerosol particle dispersion data, a quantitative microbial risk assessment was conducted for scenarios with an infectious person expelling SARS-CoV-2 virions in aerosol particles by breathing and speaking. Effects of flight conditions were evaluated using Generalized Additive Mixed Models.

Results On a typical flight with an average shedder, mean risk of contracting COVID-19 ranged from 1.3×10-3 to 9.0×10-2 . Risk increased to 7.7×10-2 with a super shedder (<3% of cases) on a long flight. Risks increased with increasing flight duration: 2 – 23 cruise flights of typical duration and 2 – 10 flights of longer duration resulted in at least 1 case of COVID-19 due to onboard aerosol transmission by one average shedder and in the case of one super shedder, at least 1 case in 1 – 3 flights of typical duration cruise and 1 flight of longer duration. Risk decreased with increasing distance from the infectious person and this decrease varied with direction. A face mask reduced emission of the larger aerosol particles and altered the direction of the aerosol particles.

Discussion From this study it can be concluded that although ventilation strongly reduces the risk of contracting COVID-19 by aerosol transmission in an aircraft cabin, residual aerosol particles containing virus continue to pose a risk. Obviously, testing before boarding will help reduce the chance of a (super)shedder boarding an aircraft and mask use further reduces aerosol transmission in the aircraft cabin.