Written by Charlotte Rigby
“SARS-COV-2 was already spreading in France in late December 2019” – A Scientific Perspective.
A French study has recently made the claim that SARS-CoV-2, the causative agent of COVID-19, was detected in France on December 27th after re-testing samples from patients diagnosed with unknown pneumonias. A single sample, belonging to a French man, tested positive for SARS-CoV-2 DNA multiple times by PCR.
Figure 1: The original paper published in ‘International Journal of Antimicrobial Agents’.
Does this explicitly mean he had COVID-19?
Not necessarily, however, more evidence is required before drawing any final conclusions. The claim is based on a PCR experiment which suggested segments of the SARS-CoV-2 genome were present in this sample. False positives can occur in this type of experiment. The investigators compensate for this by running the PCR twice. Other methods the investigators could have used to further validate this claim include are viral genome sequencing, use of phylogeny to study how closely related this viral genome is to others that the science community have sequenced and finally serology, to detect antibodies that would have been produced by the immune system during infection.
Sequencing is the process of determining the sequence of nucleotides within DNA or RNA. Knowing this can mean the virus can be compared to ‘reference genomes’ of other viruses to see if there is a match. This sequence can also be used to construct phylogenetic trees which show the evolutionary relationships between organisms, including viruses. The more closely related the virus is the more similar it usually is. These methods would show that the virus was present in the sample and also confirm where the virus belonged on the evolutionary tree, allowing scientists to pinpoint whether this virus was closely related to the viruses observed at the beginning of the outbreak.
Finally, serological evidence would prove that infection had occurred. Serological evidence is based on antibodies, a protein produced during the innate immune response to neutralise pathogens. The presence of RNA doesn’t necessarily mean infection (see the recent stir created by RNA being detected in dogs for example), antibody production does as it proves an immune response was mounted. Scientists would require a blood sample from this patient, many different tests can be performed but for SARS-CoV-2 it’s likely a simple colour change test would be used – similar to a pregnancy test(1).
Figure 2: Methods for validating identities of infectious diseases.
So, should we discount the study?
No, we shouldn’t. A result is still a result and knowledge of this is important. However, when information isn’t communicated well, or an incomplete picture is presented a wave of misinformation can occur. It’s important now more than ever to think critically about information and our sources of information. Ultimately, this is what the Science Social is about – communicating science with non-scientists and encouraging critical thinking.
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1. Amanat F, Stadlbauer D, Strohmeier S, Nguyen T, Chromikova V, McMahon M, et al. A serological assay to detect SARS-CoV-2 seroconversion in humans. medRxiv [Internet]. 2020 Jan 1;2020.03.17.20037713. Available from: http://medrxiv.org/content/early/2020/04/16/2020.03.17.20037713.abstract