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Didn't have a chance to discuss this yesterday, but I think it emphasizes again just what is still unknown about "asymptomatic" infections: a thread. (Link to research paper: https://www.nature.com/articles/s41591-020-0965-6.pdf) https://www.npr.org/sections/goatsandsoda/2020/06/23/864536258/we-still-dont-fully-understand-the-label-asymptomatic
First, we generally rely on people to self-report symptoms. This introduces biases: some people may be more "in tune" with their bodies & notice very minor symptoms. Some might not have access to a thermometer--how to know if they had fever? Not as straightforward as it seems. /2
This paper looked at 37 "asymptomatic" individuals. 60 were initially examined as lacking symptoms, but 23 ended up having symptoms dx'd by doc at enrollment or within next few days. Which brings us back to self-reporting: symptoms underestimate the severity of the disease. /3
For those 37, they did a bunch of bloodwork & radiology. Unclear if there is overlap in patients mentioned, but several had findings in bloodwork suggestive of ongoing infection, & 21 had abnormal chest CT scans (ground glass opacities and other findings). /4
They also did repeated measures of viral load by PCR (note: *they did not culture live virus*). Viral load per Ct value was similar in asymptomatic group & second group of symptomatic individuals--so there didn't seem to be a big difference in amount of virus present... /5
...but asymptomatic individuals remained positive by this measure for a longer period of time than symptomatic individuals. Again, this is just by measure of viral RNA--whether this means they are actually infectious longer wasn't tested. /6
Looking at antibodies produced, most of the asymptomatic group produced IgG, but at lower levels than symptomatic patients. Slightly fewer produced IgM, & asymptomatic people seemed to become seronegative for IgG more quickly than those with symptoms. /7
They also looked at cytokine response in both groups, and suggested collectively that asymptomatic individuals had lower cytokine responses than those with symptoms (which could drive symptoms like fever, etc.--not too surprising and data are kind of messy here). /8
So of their total of 178 confirmed positive individuals, 37 (20.8%) of those followed over time showed no clear symptoms, but had several abnormalities clinically and most had a response to infection (cytokine &/or antibody production, some w/ lung pathology). /9
Why is this important? Remember we know very little re: long-term effects of infection. I'm most concerned about those lung findings, but also (not tested here) possibility of long-term neurological sequelae. We just don't know what will happen with survivors, symptoms or no. /10
This study also didn't address transmission. Longer time positive for viral RNA suggests asymptomatic individuals may have extended ability to transmit, but that could also just be dead virus. Can't really draw conclusions from this data so this remains a huge open question. /fin
