What should be one of the hottest topics is being widely ignored by the media. A large number of positive tests reflect non-infectious individuals and most states are not identifying what proportion of tests meet the criteria of infectiousness. And clinicians need more information about the level of virus because it is relevant to clinical outcomes. Here are some additional studies on the topic.
This paper was a meta-review of research on viral load and disease severity. (Medrxiv Paper) A total of 14 studies were included. Viral loads were said to be higher in saliva and sputum than in nasal swabs. The median cycle numbers were slightly lower in asymptomatic patients and those with severe disease. 173 patients in total were studied, with multiple specimens from many. Viral loads declined as the day of sample collection was further from the date of first symptom. The median cycle number was 31, so half the samples were above that, indicating lower likelihood of viable virus.
And here is a specific study of viral load and culture positivity. (CID Article) The researchers looked at 90 samples which tested positive by PCR and were obtained at various times from onset of symptoms and thereafter. No positive culture occurred after 8 days from the day of symptom onset. Culture positivity was more likely to happen with samples closer to the day of symptom onset. Lower cycle numbers were strongly associated with positive cultures. Here is the primary quote: “infectivity (as defined by growth in cell culture) is significantly reduced when RT-PCR Ct values are > 24.” So we have labs and states using tests with cycle numbers as high as 40. That is ridiculous. All PCR tests should be reported with cycle number and with the date the test was taken compared to the date of symptom onset. Period, no excuse for not doing this, other than obfuscation.
This study covered viral load, shedding and infectiousness. (BMJ Article) It comes from Italy and looked solely at use of PCR tests to determine that there was no viral shedding, on over 1160 symptomatic patients. According to this study, viral clearance occurred within a median of 30 days in only 61% of the patients. 20% of patients who were negative on one test, were found positive on a repeat test, showing you how unreliable PCR testing is. I am covering this study to show you how failing to provide a full picture leads to bad decisions. The was no attempt to determine if the virus was viable, so the study tells us nothing about actual infectiousness. If you just read the story, you would think that a lot of people are infectious up to at least 30 days after diagnosis. But we know from other research that no one has shown shedding of viable virus much more than a week after symptom development. And these authors don’t even attempt to describe cycle number distribution for the positive tests, so we can’t make inferences about how many of these patients had viable virus. This is a worthless study, it tells you nothing. I don’t understand researchers doing any work involving positive PCR tests without telling us something about cycle number and like virus viability.