I am giving a talk on "SARS-CoV-2 testing and Immunity" this week. Thought it would make a good #Tweetorial.

Thread/
First testing.

You can categorize testing as follows:

https://abs.twimg.com/emoji/v2/... draggable="false" alt="✅" title="White heavy check mark" aria-label="Emoji: White heavy check mark">Pathogen based (test for presence of virus)

https://abs.twimg.com/emoji/v2/... draggable="false" alt="✅" title="White heavy check mark" aria-label="Emoji: White heavy check mark">Host based (test for patient& #39;s response)
There have been a LOT of Emergency Use Authorizations granted by the FDA. For a variety of tests.
Here are the types of tests that detect virus.

https://abs.twimg.com/emoji/v2/... draggable="false" alt="✅" title="White heavy check mark" aria-label="Emoji: White heavy check mark">Molecular/Genetic (RT-PCR)
https://abs.twimg.com/emoji/v2/... draggable="false" alt="✅" title="White heavy check mark" aria-label="Emoji: White heavy check mark">Antigen
https://abs.twimg.com/emoji/v2/... draggable="false" alt="✅" title="White heavy check mark" aria-label="Emoji: White heavy check mark">Viral culture
Host-based test look for antibodies against virus that are produced due to your adaptive immune response.

Either IgG or IgM.
Here is a graphic that explains the difference between a RT-PCR and Antibody test.
RT-PCR tests are the most commonly available test out there currently. Typically requires a nasopharyngeal sample.
They target a variety of RNA genes.

https://abs.twimg.com/emoji/v2/... draggable="false" alt="✅" title="White heavy check mark" aria-label="Emoji: White heavy check mark">envelope (env)
https://abs.twimg.com/emoji/v2/... draggable="false" alt="✅" title="White heavy check mark" aria-label="Emoji: White heavy check mark">nucleocapsid (N)
https://abs.twimg.com/emoji/v2/... draggable="false" alt="✅" title="White heavy check mark" aria-label="Emoji: White heavy check mark">spike (S)
https://abs.twimg.com/emoji/v2/... draggable="false" alt="✅" title="White heavy check mark" aria-label="Emoji: White heavy check mark">RNA-dependent RNA polymerase (RdRp)
https://abs.twimg.com/emoji/v2/... draggable="false" alt="✅" title="White heavy check mark" aria-label="Emoji: White heavy check mark">ORF1 genes.
RT-PCR detects genetic material. Fragments. That& #39;s it.

How long can you you have a positive RT-PCR test?

This study reported as long as 8 days after resolution of symptoms. https://www.nature.com/articles/s41591-020-0869-5">https://www.nature.com/articles/...
However, you know from my recent tweet that there are many people out there who have seen positive RT-PCRs for much longer periods. Beyond 50 days even. https://twitter.com/chungk1031/status/1258843412129705984?s=20">https://twitter.com/chungk103...
Does this mean you are infectious that entire time?

No.

What test can determine if we have active (whole) virus?

Nothing commercially available. You have to do this in a lab via cell culture.

https://wwwnc.cdc.gov/eid/article/26/6/20-0516_article">https://wwwnc.cdc.gov/eid/artic...
There is a report that demonstrates active virus via cell culture cannot be isolated from the respiratory system after about 8 days. https://www.nature.com/articles/s41586-020-2196-x">https://www.nature.com/articles/...
How about antibodies?

Here& #39;s a pre-print with good info on IgM and IgG.

https://www.medrxiv.org/content/10.1101/2020.03.24.20042382v1">https://www.medrxiv.org/content/1...
As you can see. Not everyone mounts the same antibody response. Some strong. Most weak. Some not much at all.

Who& #39;s protected? And for how long?

Unknown.
That& #39;s why the WHO issued this statement.

"There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection." https://www.who.int/news-room/commentaries/detail/immunity-passports-in-the-context-of-covid-19">https://www.who.int/news-room...
Check out this amazing artwork on sensitivity, specificity, PPV, and NPV.

https://twitter.com/stefantigges/status/1260168301436719104?s=21">https://twitter.com/stefantig... https://twitter.com/StefanTigges/status/1260168301436719104">https://twitter.com/StefanTig...
You can follow @chungk1031.
Tip: mention @twtextapp on a Twitter thread with the keyword “unroll” to get a link to it.

Latest Threads Unrolled: