Long distance airborne transmission of SARS-CoV-2: rapid systematic review

Abstract

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.

Early estimates of the incidence trend and the reproductive number of the monkeypox epidemic in Brazil

“…It is important to highlight that MPXV and SARS-CoV-2 have significant differences in the predominant transmission routes. SARS-CoV-2 can be transmitted by exposure to small droplets and aerosols in short and long distances from the emission source [ [22] , [23] , [24] ], while MPXV can be transmitted by close contacts, especially with skin lesions, such as intimate or prolonged face-to-face contact, as well as by touching surfaces and objects with viable viral particles [ [25] , [26] , [27] , [28] , [29] ]. Nevertheless, the comparable Rt values could be explained by different combinations of the determinants of the reproductive number (duration of the infectious period, rate of contacts and the transmission probability) [ 30 ].…”

Airborne SARS-CoV-2

“…And so the debate smoulders on, as Duval and colleagues (doi:10.1136/bmj-2021-068743) report from their linked systematic review supporting the role of long distance airborne transmission of SARS-CoV-2 2. The review examined covid-19 transmission events in a variety of indoor community settings ranging from fitness facilities, offices, buses, and restaurants to choir venues and a church, but not hospitals, hospices, or care homes 2345678. The inclusion of care home outbreaks might have strengthened overall findings, along with more recent studies detailing nosocomial clusters among vaccinated healthcare workers 910…”

“…But a role clearly exists for detailed epidemiology in respiratory outbreaks, simply because it provides empirical validation that aerosol transmission occurs, and in fact occurs extensively 22. As Duval and colleagues surmise, there is a need to develop a new framework for evidence synthesis of outbreak investigations 22425. Either that, or more than a century of detailed epidemiological work identifying the cause of disease outbreaks and tracking the spread of notable pathogens must be ignored.…”

Death and ill health by order of the Supreme Court

“…89 Other priorities are at play when major national drug regulators and “independent advisers” are funded extensively by the industry and make decisions that unduly favour it, as our new investigation shows (doi:10.1136/bmj.o1538). 10 Which priorities drive the reluctance to accept the evidence on airborne transmission of SARS-CoV-2, to which we add a new review (doi:10.1136/bmj-2021-068743, 10.1136/bmj.o1408)?1112 Are they related to the commercial and legal missteps in protecting healthcare professionals?…”