Transmission of SARs-CoV-2

Reference WHO registration No 2020/1077093.

The World Health Organisation 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 WHO guidance and scientific documents. CH, AP and ES also receive funding support from the NIHR SPCR Evidence Synthesis Working Group project 390.

The WHO updates interim guidance (12 July 2021) on infection prevention and control (IPC) during health care when coronavirus disease (‎COVID-19)‎ is suspected or confirmed, and cites CEBM work on airborne, finite and close contact transmission as well as non pharmaceutical interventions.

Intended for health workers, including managers and IPC teams at facility, national and district/provincial levels, this guidance summarizes evidence on infection prevention and control strategies and measures associated with the care for suspected or confirmed cases of COVID-19 in health facilities. 

Context

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.  

Dissemination

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

Additional authors

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

Elena Cecilia Rosca, Associate Professor, Department of Neurology, Victor Babes University of Medicine and Pharmacy of Timisoara