SARS-CoV-2 transmission is a very important topic to learn about so the proper protective measures can be done. Viral RNA is usually identified by using the oropharyngeal swabs, so it is important to understand the possibility of SARS-CoV-2 transmission through blood, especially considering the antibody tests are happening in big numbers right now. In their new research, British scientists analyzed blood samples of people infected with COVID-19 and historic data to understand the patterns of viral RNA appearing in blood and if it correlates with the virus still being alive.
212 blood samples were collected from 167 people either infected with SARS-CoV-2 or already recovered from it. Additionally, 212 blood samples were collected from volunteer plasma donors, more than 28 days after they recovered from the symptoms. PCR test showed the presence of viral RNA in 27 samples (12.7%) gotten from 20 patients. Viral RNA detection was associated with a more severe disease state and was only present up to day 20 post symptom onset.
Past researches on the topic were also analyzed (22 out of 28 researches on the topic were fitting for meta-analysis) and confirmed the correlation between the disease severity and the viral load presence. According to the combined data, the frequency of viral RNA presence 28 days from symptom onset is about 10%.
Ct values for all of 27 PCR-positive patients were high (median 40.9) and only in 7 samples, Ct was lower than 37 (the threshold value for positive test result). High Ct values reflect low copy numbers and suggest that assays may be detecting genomic fragments rather than replication-competent virus in blood.
Researches also analyzed the PCR-positive serum's ability to infect other cells. However, cytopathic effects only arose in cell cultures inoculated with reference viral stock, but not in samples from COVID-19 patients or pre-pandemic controls, so there no proof of replication-competent virus' presence was gotten.
Thus, we can conclude that viral RNA load correlates with the severity of the disease, but there is no evidence that blood samples with RNA loads contain the virus that can still replicate. Those facts indicate that the risk of SARS-CoV-2 transmission by contact with those samples is minimal.