Systematic Review of the Key Factors Influencing the Indoor Airborne Spread of SARS-CoV-2

Abstract

The COVID-19 pandemic due to the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) has been plaguing the world since late 2019/early 2020 and has changed the way we function as a society, halting both economic and social activities worldwide. Classrooms, offices, restaurants, public transport, and other enclosed spaces that typically gather large groups of people indoors, and are considered focal points for the spread of the virus. For society to be able to go "back to normal", it is crucial to keep these places open and functioning. An understanding of the transmission modes occurring in these contexts is essential to set up effective infection control strategies. This understanding was made using a systematic review, according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses statement (PRISMA) 2020 guidelines. We analyze the different parameters influencing airborne transmission indoors, the mathematical models proposed to understand it, and discuss how we can act on these parameters. Methods to judge infection risks through the analysis of the indoor air quality are described. Various mitigation measures are listed, and their efficiency, feasibility, and acceptability are ranked by a panel of experts in the field. Thus, effective ventilation procedures controlled by CO₂-monitoring, continued mask wearing, and a strategic control of room occupancy, among other measures, are put forth to enable a safe return to these essential places.

Keywords: CO2; COVID-19; SARS-CoV-2; air quality; airborne transmission; indoor; mitigation measures.

Figure 1

Flowchart representing the record selection process according to the PRISMA guidelines [22].

Figure 2

Origin of publications included in this systematic review (A), and publication activity by year of records screened (B).

Figure 3

(A) Efficacy, (B) feasibility, and (C) acceptability of the considered measures. Legend: The line inside each rectangle represents the median of the score distribution between the different experts; the solid lines below and above each rectangle represent, respectively, the first and the third quartiles; adjacent lines to the whiskers represent the limits of the 95% confidence interval; small circles represent outside values. ID of the measure considered are numbers of mitigation measures that were presented in the second column of Table 4.