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Thoughts on upcoming #COVID19 #serology tests:
This is actually quite a challenge! (#Diagnostics often involve a lot of complexities). There is a lot of pressure to roll these tests out, but they need to perform well, or we do more harm than good. #MicroRounds (A thread)
WHY we need these soon:
1. Contact tracing.
2. Can be used to test if a vaccine is working during a clinical trial (70 of them ongoing right now, I believe)
3. Inform public policy makers about rate of asymptomatic cases + previous infections/exposures =informed decision making
How is developing a #PCR different than developing a #serology test?
1. #PCR tests detect viral RNA/DNA (in this case RNA) and can be pretty straight-forward in terms of development
2. #Serology relies on knowing about the #SARSCoV2 structure and how the human body responds.
When someone becomes infected with #SARSCoV2 , their immune system will respond to proteins (antigens) on the viral coat, and subsequently form antibodies against these (in theory). In the case of #SARSCoV2, that pretty little spike protein is the most obvious choice...
But as described in this Lancet article (…), it's not that straight forward. There are several parts of the spike protein that could be used to develop a #diagnostic #test. Which one is best? The answer is likely whichever part of the virus is most UNIQUE:
It is important to remember that while this virus is "closest" to SARS, there are 4 seasonal #coronaviruses that circulate and give us colds every year (not 19, despite what the white house says). Having cross-reactivity with any of these would be a bad thing...
Once the viral protein that will be used for a test is decided on, it has to be produced in the lab. That, in itself, is not particularly easy either.
So, for all those out there screaming, "I don't care, I just want to be tested!!", what are the consequences of a bad test?
1. Having #SARS_CoV2 antibodies doesn't necessarily mean you're #immune. How long do the antibodies stay? Do they protect from #reinfection?
2. False positives: people are wrongly re-assured. They return to work, school, life...potentially spreading disease.
Importantly, the specificity of these tests matters and it matters WHICH populations you test. Using these tests in populations where the #prevalence of #COVID19 is low can be problematic. Check out the calculator on this site to play with the numbers:…
Once these tests are available, their suggested use needs to be explained well. This is where #diagnostic #stewardship comes into play. These tests will likely not be helpful for acute infection, and the timing of testing will be important to detect IgG...
For example, this study (…)
demonstrates that reliable IgG seroconversion didn't happen until 2 weeks after disease onset (although this seroconversion has remained difficult to determine).
There is a lot more to unpack here, but it's important to remember that with #diagnostics, simply having the test is not enough. We have to shift our mentality away from, "there's a drug, let's use it!" and "There's a test, let's use it!" Doing this often leads to additional harm
It is the perfect time to lean into your infectious disease, microbiology and diagnostics experts at this time.
#IDtwitter #MedTwitter #MedEd @ASCLS @RodneyRohde @odie0222 @richdavisphd @ASMicrobiology @JClinMicro @GermHunterMD @SJLovesMicro #Laboratory @jesscataldi
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