Abstract

VELARDE, Fernando; MAMANI-PACO, Rubén  and  ANDRADE-FLORES, Marcos. Estimation of the probability of contagion of covid-19 by aerosols in closed environments: Applications to cases in the city of La Paz, Bolivia. Revista Boliviana de Física [online]. 2020, vol.37, n.37, pp.22-30. ISSN 1562-3823.

Abstract Since the arrival of the SARS-CoV-2 coronavirus, health entities published recommenda-tions to avoid the spread of COVID-19. The most important ones are related to avoiding pos-sible contagión through contaminated surfaces (fomites) and the deposition of saliva droplets in the eyes, nose or mouth. However, observational and theoretical evidence suggests that in closed environments the most important form of contagión is related to infectious respiratory aerosols. In this work a mathematical model is used to estimate the probability of contagión by these aerosols in closed environments. This model is applied to three cases: a classroom, a theater, and public transportation vehicles in the city of La Paz, Bolivia. The results showed that the probability of contagión of COVID-19 strongly depends on the exposure time (duration of events) and the ventilation of the environments. The longer the duration of an event and the poorer the ventilation of the environment, the greater the probability of contagión. Additionally, carbón dioxide concentration was measured as a proxy for indoor air quality, in terms of aerosol concentration, and to establish ventilation levéis in some of the closed environments studied. The results of the model applied to the classroom indicate that the probability of contagión in the case of a two-hour class and an asymptomatic carrier (instructor) is of the order of 10%, while in the case of the theater the probability of contagión is of the order of 25% for the studied event. Finally, in the case of minibuses, the most used means of public transport in Bolivia, the probability of contagión for 60-minute trips ranges between 19% and 97% depending on the number of passengers who are infected (between one to six in this study) and, fundamentally, on the ventilation that depends on whether the windows of the vehicle are closed or open.

Keywords : Aerosols; diseases; probability of contagión.

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