Airborne transmission of biological agents within the indoor built environment: a multidisciplinary review

Abstract

The nature and airborne dispersion of the underestimated biological agents, monitoring, analysis and transmission among the human occupants into building environment is a major challenge of today. Those agents play a crucial role in ensuring comfortable, healthy and risk-free conditions into indoor working and leaving spaces. It is known that ventilation systems influence strongly the transmission of indoor air pollutants, with scarce information although to have been reported for biological agents until 2019. The biological agents' source release and the trajectory of airborne transmission are both important in terms of optimising the design of the heating, ventilation and air conditioning systems of the future. In addition, modelling via computational fluid dynamics (CFD) will become a more valuable tool in foreseeing risks and tackle hazards when pollutants and biological agents released into closed spaces. Promising results on the prediction of their dispersion routes and concentration levels, as well as the selection of the appropriate ventilation strategy, provide crucial information on risk minimisation of the airborne transmission among humans. Under this context, the present multidisciplinary review considers four interrelated aspects of the dispersion of biological agents in closed spaces, (a) the nature and airborne transmission route of the examined agents, (b) the biological origin and health effects of the major microbial pathogens on the human respiratory system, (c) the role of heating, ventilation and air-conditioning systems in the airborne transmission and (d) the associated computer modelling approaches. This adopted methodology allows the discussion of the existing findings, on-going research, identification of the main research gaps and future directions from a multidisciplinary point of view which will be helpful for substantial innovations in the field.

Keywords: Airborne transmission; Bioaerosols; Building ventilation; CFD models; Droplets; Indoor air quality.

Fig. 1

Schematic representation of a variety of biological (infectious) and chemical agents’ transmission between humans via the airborne route

Fig. 2

Schematic representation of the vibrational, transitional and bag deformation shape changes of water droplets travelling in air adapted from (Soni et al. 2020)

Fig. 3

The size ranges of air particles and microorganisms

Fig. 4

A donor-recipient model of transmission of respiratory pathogens within droplets

Fig. 5

Images of key respiratory pathogens: a SARS-CoV-2, b Mycobacterium tuberculosis and c Aspergillus fumigatus. Source: Public Health Image Library, CDC-USA

Fig. 6

Displacement downward ventilation pattern

Fig. 7

Displacement upward ventilation pattern

Fig. 8

Mixed ventilation (MV) pattern

Fig. 9

Underfloor air distribution pattern

Fig. 10

Building layout produced by CONTAM according to available HVAC data Reproduced from Reference (Argyropoulos et al. 2017a, b) with permission from Elsevier

Fig. 11

Visualisations demonstrating the effect of particle size (and mass) on the modelled spreading of the cough-released aerosol cloud. For better sense of scale, bystanders are placed 8 m from the coughing person. Instantaneous views on the state of the cloud are shown for realisations where the particles have a no mass, b 1000 kg m⁻³ density and 10-μm diameter and c 1000 kg m⁻³ density and 20-μm diameter. Images on the left column are at t = 20 s and on the right column at t = 120 s. Below, d presents the time evolution of the mean elevation of the 99th percentile concentration highlighting the different descent rates. Droplets in these size scales have τ_evap < 1 s and they would become aerosol-like droplet nuclei very rapidly. Reproduced from Reference (Vuorinen et al. 2020) with permission from Elsevier

Fig. 12

Schematic of the computational domain with two virtual humans and the hybrid mesh details. Reproduced from Ref (Feng et al. 2020a, b) with permission from Elsevier

Fig. 13

Prospective view of the Scenarios A, B and C at t = 1 s (left) and 5 s (right). The spheres represent the droplets coloured by the diameter size (top right legend). The contaminated air is represented by different iso-surfaces coloured by mass fraction. Reproduced from Reference (Feng et al. 2020a, b) with permission from Elsevier

Fig. 14

Simulated evolution of the 10-µm saliva particulate concentration (volume fraction) after the cough under outdoor conditions (mild breeze) without (top) and with (bottom) the facial mask. [(a) and (f)], [(b) and (g)], [(c) and (h)], [(d) and (i)] and [(e) and (j)] show the simulated saliva particulate concentration fields after 0.24 s, 0.3 s, 0.4 s, 0.5 s and 0.6 s, respectively, on the sagittal plane. The outdoor simulations were stopped after 0.6 s, when the saliva particulates travel ∼2.0 m and 2.2 m without (top) and with (bottom) the facial mask, respectively. Reproduced from Reference (Khosronejad et al. 2020) with permission from AIP

Fig. 15

The framework of the multiscale CFPD-HCD model for the human-to-human IAV infection with a subject-specific airway geometry. The description of the HCD model is given in the ‘The human respiratory system’ section of the original paper (Haghnegahdar et al. 2019a). The detail of the final polyhedral-core mesh is provided at the right nostril and an airway outlet (RUL: right upper lobe, RML: right middle lobe, RLL: right lower lobe, LUL: left upper lobe, LLL: left lower lobe). Reproduced from Reference (Haghnegahdar et al. with permission from Elsevier