Objectives To evaluate the potential for long distance airborne transmission of SARS-CoV-2 in indoor community settings and to investigate factors that might influence transmission. Design Rapid systematic review and narrative synthesis. Data sources Medline, Embase, medRxiv, Arxiv, and WHO COVID-19 Research Database for studies published from 27 July 2020 to 19 January 2022; existing relevant rapid systematic review for studies published from 1 January 2020 to 27 July 2020; and citation analysis in Web of Science and Cocites. Eligibility criteria for study selection Observational studies reporting on transmission events in indoor community (non-healthcare) settings in which long distance airborne transmission of SARS-CoV-2 was the most likely route. Studies such as those of household transmission where the main transmission route was likely to be close contact or fomite transmission were excluded. Data extraction and synthesis Data extraction was done by one reviewer and independently checked by a second reviewer. Primary outcomes were SARS-CoV-2 infections through long distance airborne transmission (>2 m) and any modifying factors. Methodological quality of included studies was rated using the quality criteria checklist, and certainty of primary outcomes was determined using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) framework. Narrative synthesis was themed by setting. Results 22 reports relating to 18 studies were identified (methodological quality was high in three, medium in five, and low in 10); all the studies were outbreak investigations. Long distance airborne transmission was likely to have occurred for some or all transmission events in 16 studies and was unclear in two studies (GRADE: very low certainty). In the 16 studies, one or more factors plausibly increased the likelihood of long distance airborne transmission, particularly insufficient air replacement (very low certainty), directional air flow (very low certainty), and activities associated with increased emission of aerosols, such as singing or speaking loudly (very low certainty). In 13 studies, the primary cases were reported as being asymptomatic, presymptomatic, or around symptom onset at the time of transmission. Although some of the included studies were well conducted outbreak investigations, they remain at risk of bias owing to study design and do not always provide the level of detail needed to fully assess transmission routes. Conclusion This rapid systematic review found evidence suggesting that long distance airborne transmission of SARS-CoV-2 might occur in indoor settings such as restaurants, workplaces, and venues for choirs, and identified factors such as insufficient air replacement that probably contributed to transmission. These results strengthen the need for mitigation measures in indoor settings, particularly the use of adequate ventilation. Systematic review registration PROSPERO CRD42021236762.

ObjectiveTo 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.DesignSystematic review and narrative synthesis.Data sourceMEDLINE, 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 selectionObservational 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 synthesisData 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.ResultsOf 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.ConclusionThis 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 registrationPROSPERO CRD42021236762

In this letter we briefly describe how we selected and implemented the quality criteria checklist (QCC) as a critical appraisal tool in rapid systematic reviews conducted to inform public health advice, guidance and policy during the COVID-19 pandemic. As these rapid reviews usually included a range of study designs, it was key to identify a single tool that would allow for reliable critical appraisal across most experimental and observational study designs and applicable to a range of public health topics. After carefully considering a number of existing tools, the QCC was selected as it had good interrater agreement between three reviewers (Fleiss kappa coefficient: 0.639) and was found to be easy and fast to apply once familiar with the tool. The QCC consists of 10 questions, with sub-questions to specify how it should be applied to a specific study design. Four of these questions are considered as critical (on selection bias, group comparability, intervention/exposure assessment and outcome assessment) and the rating of a study (high, moderate or low methodological quality) depends on the responses to these four critical questions. Our results suggest that the QCC is an appropriate critical appraisal tool to assess experimental and observational studies in systematic or rapid reviews and that it can be used in a range of public health topics.

In this letter, we briefly describe how we selected and implemented the quality criteria checklist (QCC) as a critical appraisal tool in rapid systematic reviews conducted to inform public health advice, guidance and policy during the COVID-19 pandemic. As these rapid reviews usually included a range of study designs, it was key to identify a single tool that would allow for reliable critical appraisal across most experimental and observational study designs and applicable to a range of topics. After carefully considering a number of existing tools, the QCC was selected as it had good interrater agreement between three reviewers (Fleiss kappa coefficient 0.639) and was found to be easy and fast to apply once familiar with the tool. The QCC consists of 10 questions, with sub-questions to specify how it should be applied to a specific study design. Four of these questions are considered as critical (on selection bias, group comparability, intervention/exposure assessment and outcome assessment) and the rating of a study (high, moderate or low methodological quality) depends on the responses to these four critical questions. Our results suggest that the QCC is an appropriate critical appraisal tool to assess experimental and observational studies within COVID-19 rapid reviews. This study was done at pace during the COVID-19 pandemic; further reliability analyses should be conducted, and more research is needed to validate the QCC across a range of public health topics.