Modeling the factors that influence exposure to SARS-CoV-2 on a subway train carriage.

Daniel Miller,Ursula Dalrymple,Marco‐Felipe King,Catherine J Noakes,Martín López‐García,James Nally,Ian Hall,Simon T Parker,Joseph R Drodge,Gary I Reeves,Henry Cooper,Andrew M Bate

doi:10.1111/ina.12976

Daniel Miller, Ursula Dalrymple + Show 10 more

Open Access

https://doi.org/10.1111/ina.12976

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Abstract

We propose the Transmission of Virus in Carriages (TVC) model, a computational model which simulates the potential exposure to SARS‐CoV‐2 for passengers traveling in a subway rail system train. This model considers exposure through three different routes: fomites via contact with contaminated surfaces; close‐range exposure, which accounts for aerosol and droplet transmission within 2 m of the infectious source; and airborne exposure via small aerosols which does not rely on being within 2 m distance from the infectious source. Simulations are based on typical subway parameters and the aim of the study is to consider the relative effect of environmental and behavioral factors including prevalence of the virus in the population, number of people traveling, ventilation rate, and mask wearing as well as the effect of model assumptions such as emission rates. Results simulate generally low exposures in most of the scenarios considered, especially under low virus prevalence. Social distancing through reduced loading and high mask‐wearing adherence is predicted to have a noticeable effect on reducing exposure through all routes. The highest predicted doses happen through close‐range exposure, while the fomite route cannot be neglected; exposure through both routes relies on infrequent events involving relatively few individuals. Simulated exposure through the airborne route is more homogeneous across passengers, but is generally lower due to the typically short duration of the trips, mask wearing, and the high ventilation rate within the carriage. The infection risk resulting from exposure is challenging to estimate as it will be influenced by factors such as virus variant and vaccination rates.

Highlights

The COVID-19 pandemic has caused huge economic and societal impacts worldwide, and the suppression of its transmission has become a globally sought and increasingly critical goal as many healthcare systems approach capacity and capability limits
The median values reflect a different picture, where airborne dose is higher than both the close-range and the fomite doses (3.5 x 10–8 vs. 0)
At the 1% prevalence level, the number of 0-doses dominates the median values suggesting that the mean values are heavily affected by infrequent or opportunistic events, represented by the outliers, for the close-range and the fomite routes

Summary

Introduction

The COVID-19 pandemic has caused huge economic and societal impacts worldwide, and the suppression of its transmission has become a globally sought and increasingly critical goal as many healthcare systems approach capacity and capability limits. Understanding the locations where transmission happens, the routes of transmission, and the effectiveness of different mitigation measures is important for enabling safer societal interactions. The SARS-CoV-2 virus is released in droplets and aerosols carrying the virus during respiratory activities including breathing, talking, and coughing. At close-range (2 m). Fomite transmission may occur through contact with contaminated surfaces and subsequent touching of mucous membranes. The relative contribution of these different routes is unknown, risk factors that have been identified include duration of time spent with infected people, close proximity, activities that may generate more aerosol, and enclosed poorly ventilated environments.[1]

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