In a recent article posted to the medRxiv* preprint server, researchers presented the protocol for a systematic review assessing viral cultures for airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
Study: Viral Cultures for Assessing Airborne Transmission of SARs-CoV-2: a Systematic Review Protocol (version 1). Image Credit: Design_Cells/Shutterstock
The dissemination of respiratory droplets containing infectious microorganisms, which remain infectious when suspended in the air for a long time and distance, leads to airborne transmission of an infectious agent. Given the extensive global impact of the ongoing coronavirus disease 2019 (COVID-19) pandemic and the high transmissibility of the new SARS-CoV-2 variants, there is a pressing need to obtain robust evidence on the airborne transmission potential of SARS-CoV-2.
Previous systematic reviews
The researchers of the present study recently conducted a systematic review of 67 primary studies and 22 reviews on the airborne transmission of SARS-CoV-2 to identify, assess and summarize the evidence regarding the same.
The studies included were low quality, lacked standardized techniques, and were observational. A total of 10 studies attempted viral culturing but failed to draw any firm conclusions due to the absence of recoverable SARS-CoV-2 in the cultures. The remaining reviews indicated a lack of evidence to support SARS-CoV-2 airborne transmission. Most primary studies identified the ribonucleic acid (RNA) of SARS-CoV-2 in the air but failed to detect the infectious SARS-CoV-2.
The researchers then conducted a systematic review that evaluated the transmission and infectious potential of SARS-CoV-2 asymptomatic patients. This review used data from studies with viral culture, serial polymerase chain reaction (PCR) cycle threshold (Ct) values and gene sequencing. Probable evidence regarding SARS-CoV-2 transmission from asymptomatic and presymptomatic patients was obtained from these high-quality studies, along with additional information from the authors of these studies.
Soon after the publication of this systematic review, several new studies targeting airborne SARS-CoV-2 transmission were published. Further, the review also derived a framework to obtain robust evidence regarding the transmission of infectious respiratory agents.
Framework for a future systematic review
In the future, the researchers intend to conduct a systematic review evaluating the proof for the airborne transmission of SARS-CoV-2 through high-quality studies confirming infection using longitudinal serial PCRs or viral cultures with or without gene sequencing. This research aims to determine if airborne SARS-CoV-2 samples are infectious. If yes, the researchers further plan to evaluate the proportion required for SARS-CoV-2 to be infectious in the air, the time and distance it remains infectious in the air, the correlation between airborne PCR ct values and the infectiousness of the sample, any instances of chain transmission providing actual proof for SARS-CoV-2 airborne transmission, and the circumstances required for SARS-CoV-2 to remain infectious in the air for long distances.
Only studies with serial quantitative reverse transcription-PCR (qRT-PCR), or viral culture, with or without genomic sequencing will be included in the systematic review whereas, modeling or predictive studies will be excluded.
An information specialist-driven search of medRxiv, LitCovid, World Health Organization (WHO) COVID-19, and Google Scholar databases using keywords such as airborne, aerosol, and droplet from September 10, 2020, to December 30, 2021, has been planned to update the results of the previous reviews.
The extraction of the variables will be based on standardized data extraction and assessment template. The data extracted will include the type of study, sampling methods, study setting, and population characteristics.
Further, two reviewers will separately determine the eligibility of the studies to include in the analysis. If a discussion between the two reviewers cannot resolve any opinion differences, a third reviewer will decide the matter.
The researchers intend to use techniques from their previous review on SARS-CoV-2 asymptomatic and presymptomatic patients to determine the chain of SARS-CoV-2 transmission. According to the previous review, eligible studies were those with a documented probability of presymptomatic and asymptomatic SARS-CoV-2 transmission, sufficient monitoring and reporting of SARS-CoV-2 symptoms, and detection of infectious SARS-CoV-2 from viral culture.
To determine the quality of the included studies, the researchers intend to characterize the source population, study methods, SARS-CoV-2 samples, outcome reporting, and monitoring.
The systematic review will be conducted as per the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. If the data allows, meta-analyses and subgroup analyses will also be performed.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.