Airborne transmission of SARS-CoV-2 over distances greater than two metres: a rapid systematic review

Objective To evaluate the potential for long-distance (over two metres) airborne transmission of SARS-CoV-2 in indoor community settings and investigate factors which may impact this transmission. Design Systematic review and narrative synthesis. Data source MEDLINE, Embase, medRxiv, Arxiv and WHO COVID-19 Research Database for studies published from 27 July 2020 to 21 April 2021; existing relevant rapid systematic reviews for studies published between 1 January to 27 July 2020. Eligibility criteria for study selection Observational studies that included a thorough epidemiological assessment of routes of transmission and which reported on the likelihood of airborne transmission of SARS-CoV-2 at a distance greater than two metres in indoor community settings. Data extraction and synthesis Data extraction was completed by one reviewer and independently checked by a second reviewer. Primary outcomes were COVID-19 infections via airborne transmission over distances greater than two metres and any factors that may have modified transmission risk. Included studies were rated using a quality criteria checklist (QCC) for primary research and certainty of key outcomes was determined using GRADE. Narrative synthesis was themed by setting. Results Of the 3,780 articles screened for inclusion, 15 publications reporting on 13 epidemiological investigations were included (three high, six medium and four low quality). Airborne transmission at distances greater than two metres was likely to have occurred for some or all transmission events in 12 studies and was unclear in one study (GRADE: very low certainty). In all studies, one or more factors plausibly increased the likelihood of long-distance airborne transmission occurring, particularly insufficient air replacement (GRADE: very low certainty), recirculating air flow (GRADE: very low certainty) and singing (GRADE: very low certainty). In nine studies, the primary cases were reported as being asymptomatic, presymptomatic or around symptom onset at the time of transmission. Conclusion This rapid systematic review found evidence of long-distance airborne transmission of SARS-CoV-2 in indoor community settings and identified factors that likely contributed to this transmission in all included studies. These results strengthen the need for adequate mitigation measures in indoor community settings, particularly adequate ventilation with fresh air, and caution required with the use of recirculating air flow systems. Systematic review registration PROSPERO CRD42021236762