Transmission of SARs-CoV-2
Providing a rapid summary and evaluation of relevant data on the transmission of SARS-CoV-2, reporting important policy implications and highlighting areas of urgently needed research.
Our multidisciplinary team has considerable expertise in evidence synthesis and the evaluation of acute respiratory infections. Carl Heneghan and Tom Jefferson lead the research and have worked together for over a decade having been authors of the Tamiflu reviews. Both are Clinical Editors for the Cochrane Acute Respiratory Infections Group.
Transmission of SARS-CoV-2
We publish updates with recommendations for policy, and a series of hypotheses to be tested by further work. We have concluded the first phase of 4 reviews on transmission causality. Our conclusions are below the byline of each review.
The transmission areas include airborne, contact and droplet, orofecal, vertical, fomite and asymptomatic and presymptomatic transmission.
SARS-CoV-2 and the role of airborne transmission: systematic review
Heneghan C; Spencer EA; Brassey J; Plüddemann A; Onakpoya I; Evans D; Conly JM; Jefferson T. [version 1] F1000Research 2021, 52091.
Conclusion: SARS-CoV-2 RNA is detected intermittently in the air in various settings. Standardized guidelines for conducting and reporting research on airborne transmission are needed. The lack of recoverable viral culture samples of SARS-CoV-2 prevents firm conclusions over airborne transmission.
SARS-CoV-2 and the role of orofecal transmission: systematic review
Heneghan C; Spencer EA; Brassey J; Plüddemann A; Onakpoya I; Evans D; Conly JM; Jefferson T. [version 1] F1000Research 2021, 51592
Conclusions: Varied observational and mechanistic evidence suggests SARS-CoV-2 can infect and be shed from the human gastrointestinal tract, including some limited data demonstrating viral culture in fecal samples. Future studies should test this hypothesis rigorously to allow the development of appropriate public health measures.
SARS-CoV-2 and the role of fomite transmission: systematic review
Onakpoya I; Heneghan C; Spencer EA; Brassey J; Plüddemann A; Evans D; Conly JM; Jefferson T. [version 1] F1000Research 2021, 51590
Conclusion: The majority of studies report the identification of SARS-CoV-2 RNA on inanimate surfaces; however, the lack of positive viral cultures creates uncertainty about fomites as a mode of transmission. The late timing of sample collection with respect to the illness onset and the variability in reported cycle thresholds and the relatively high values precludes drawing any firm conclusions. Heterogeneity in study designs and methodology prevents comparisons of findings across studies. Standardized guidelines for conducting and reporting research on fomite transmission is warranted.
SARS-CoV-2 and the role of close contact in transmission: systematic review
Onakpoya I; Heneghan C; Spencer EA; Brassey J; Plüddemann A; Evans D; Conly JM; Jefferson T. [version 1] F1000Research 2021
Conclusion: The evidence from published studies demonstrates that SARS-CoV-2 can be transmitted via close contact settings. The risk of transmission is greater in household contacts. There was wide variation in methodology. Standardized guidelines for reporting transmission in close contact settings should be developed to improve the quality reporting.
Systematic reviews on the modes of transmission of SARS-CoV-2
Reference WHO registration No 2020/1077093.
The WHO funded reviews were the first phase of our project. Its objective is to undertake a series of living systematic searches and appraisal of evidence on SARS-CoV-2 modes of transmission and its related updates are informing World Health Organization guidance and scientific documents. CH, AP and ES also receive funding support from the NIHR SPCR Evidence Synthesis Working Group project 390.
Viral cultures for COVID-19
Complete live viruses are necessary for transmission, not the fragments identified by PCR. Prospective routine testing of reference and culture specimens and their relationship to symptoms, signs and patient co-factors should be used to define the reliability of PCR for assessing infectious potential. Those with a high cycle threshold are unlikely to have infectious potential.
Read the research: Viral cultures for COVID-19 infectious potential assessment – a systematic review.
What did we do?
We systematically reviewed the evidence from studies relating SARS-CoV-2 culture with the results of RT-PCR and other variables which may influence the interpretation of the test, such as time from symptom onset
PCR testing cannot distinguish between the shedding of live virus or of viral fragments with no infectious potential. Although viral culture is difficult, time-consuming and requires specialised facilities it potentially represents the best indicator of infection and infectious potential.
21st Aug: It’s a mistake to think all positive Covid tests are the same Carl Heneghan, Tom Jefferson
14th Sep: What does a case of COVID-19 really mean? Carl Heneghan, Tom Jefferson
7th Sep: Covid-19 and the end of clinical medicine as we know it Carl Heneghan, Tom Jefferson
John Conly, Professor of Medicine, Department of Medicine (Infectious Diseases), Cumming School of Medicine, University of Calgary and Alberta Health Services
David Evans, Professor, Department of Medical Microbiology & Immunology Chair
Jefferson T. et al, (2020)