This is a really important study on virus shedding in #covid19 with quite a few implications:
The researchers looked very closely at 9 #covid19 patients from the Munich cluster discovered in late January to understand when people have symptoms, shed live virus etc.
"Whereas virus was readily isolated during the first week of symptoms from a significant fraction of samples (16.66% in swabs, 83.33% in sputum samples), no isolates were obtained from samples taken after day 8 in spite of ongoing high viral loads."
This is really important, because when #covid19 case numbers rise, there will be pressure on hospitals to discharge patients as soon as possible. But when is that? When can patients be discharged without creating risk of them still spreading the disease?
This paper argues #covid19 patients "beyond day 10 of symptoms with less than 100,000 viral RNA copies per ml of sputum” can be sent home ("with ensuing home isolation”). "Both criteria predict that there is little residual risk of infectivity, based on cell culture."
And because some people keep bringing this up: "Virus isolation from stool samples was never successful, irrespective of viral RNA concentration, based on a total of 13 samples taken between days six to twelve from four patients.”
The study does not just have implications for the end of disease, but also for the beginning: Patients examined here (except one) were tested early when they had mild symptoms. Results suggest "simple throat swabs will provide sufficient sensitivity at this stage of infection”!
Authors note that this is different from #SARS: "only 38 of 98 nasal or nasopharyngeal swab samples tested positive by RT-PCR in SARS patients in Hong Kong”.
"Successful live virus isolation from throat swabs is another striking difference from SARS, for which such isolation was rarely successful”. Suggests that virus replicates in upper respiratory tract early. Later, #COVID19 "resembles SARS" replicating in lower respiratory tract.
We’ll be talking about this study more, I’m sure. For now, one more point: When patients developed antibodies, viral load did not fall sharply off. So any vaccine counting on antibodies "should aim to induce particularly strong antibody responses in order to be effective"
Usual caveats apply: This paper is on a preprint server. It has not been peer-reviewed or accepted for publication yet.
