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Review
. 2021 Apr 3:11:10002.
doi: 10.7189/jogh.11.10002.

Which factors influence the extent of indoor transmission of SARS-CoV-2? A rapid evidence review

Lara Goodwin  1 , Toneka Hayward  1 , Prerna Krishan  1 , Gemma Nolan  1 , Madhurima Nundy  1 , Kayla Ostrishko  1 , Antonio Attili  2 , Salva Barranco Cárceles  2 , Emmanuel I Epelle  2 , Roman Gabl  2 , Evanthia J Pappa  2 , Mateusz Stajuda  2 , Simone Zen  2 , Marshall Dozier  3 , Niall Anderson  1 , Ignazio M Viola  2 , Ruth McQuillan  1
Affiliations
Review

Which factors influence the extent of indoor transmission of SARS-CoV-2? A rapid evidence review

Lara Goodwin et al. J Glob Health. .

Abstract

Background: This rapid evidence review identifies and integrates evidence from epidemiology, microbiology and fluid dynamics on the transmission of SARS-CoV-2 in indoor environments.

Methods: Searches were conducted in May 2020 in PubMed, medRxiv, arXiv, Scopus, WHO COVID-19 database, Compendex & Inspec. We included studies reporting data on any indoor setting except schools, any indoor activities and any potential means of transmission. Articles were screened by a single reviewer, with rejections assessed by a second reviewer. We used Joanna Briggs Institute and Critical Appraisal Skills Programme tools for evaluating epidemiological studies and developed bespoke tools for the evaluation of study types not covered by these instruments. Data extraction and quality assessment were conducted by a single reviewer. We conducted a meta-analysis of secondary attack rates in household transmission. Otherwise, data were synthesised narratively.

Results: We identified 1573 unique articles. After screening and quality assessment, fifty-eight articles were retained for analysis. Experimental evidence from fluid mechanics and microbiological studies demonstrates that aerosolised transmission is theoretically possible; however, we found no conclusive epidemiological evidence of this occurring. The evidence suggests that ventilation systems have the potential to decrease virus transmission near the source through dilution but to increase transmission further away from the source through dispersal. We found no evidence for faecal-oral transmission. Laboratory studies suggest that the virus survives for longer on smooth surfaces and at lower temperatures. Environmental sampling studies have recovered small amounts of viral RNA from a wide range of frequently touched objects and surfaces; however, epidemiological studies are inconclusive on the extent of fomite transmission. We found many examples of transmission in settings characterised by close and prolonged indoor contact. We estimate a pooled secondary attack rate within households of 11% (95% confidence interval (CI) = 9, 13). There were insufficient data to evaluate the transmission risks associated with specific activities. Workplace challenges related to poverty warrant further investigation as potential risk factors for workplace transmission. Fluid mechanics evidence on the physical properties of droplets generated by coughing, speaking and breathing reinforce the importance of maintaining 2 m social distance to reduce droplet transmission.

Conclusions: This review provides a snap-shot of evidence on the transmission of SARS-CoV-2 in indoor environments from the early months of the pandemic. The overall quality of the evidence was low. As the quality and quantity of available evidence grows, it will be possible to reach firmer conclusions on the risk factors for and mechanisms of indoor transmission.

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Conflict of interest statement

Competing interest: The following received small honoraria for their work on this project from the DDI and ISSF3 funding sources DDI and ISSF3 funding sources indicated in the paper: Lara Goodwin; Toneka Hayward; Prerna Krishanp; Gemma Nolan; Madhurima Nundy; Kayla Ostrishko; Salva Barranco Cárceles; Emmanuel I Epelle; Evanthia J Pappa; Mateusz Stajuda The authors have completed the ICMJE competing interests form (available upon request from the corresponding author), and declare no further conflicts of interest.

Figures

Figure 1
Figure 1
PRISMA diagram.
Figure 2
Figure 2
Forest plot – pooled estimate of household secondary attack rate (SAR). I2 = 0.00%, Q(df = 3) = 1.72, P = 0.63.
See this image and copyright information in PMC

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