Thread On tests and the media

It is almost universal that any piece discussing Rapid Ag tests says “PCR is more accurate but…”

But even this isn’t true. It simply depends what you want to detect.

If wanting to identify ppl who are contagious, PCR is much less accurate.

1/
If your goal is to detect ppl are infectious, a rapid Ag test is highly sensitive AND specific for this.

PCR is not specific for this. It will read positive even when not infectious. So… it’s less accurate for the public health question at hand “am I infectious”

2/
You might say… well PCR is much more sensitive. But even that is not true. A bit more, yes, but if wanting to catch infectious ppl, it’s really but that much more sensitive and, if that’s your goal, then PCR is massively LESS effective than a rapid test.

3/
An analogy:

If I want to ask “Is my leg bone broken in half”

Sure, an MRI is technically a more sensitive technology overall, but a fast X-ray is going to be essentially 100% sensitive for the question - “is my femur in 2 pieces”

The MRI slows w/out adding much

4/
The whole reason we’re in a mess of not having enough rapid tests today is bc confusion surrounding their utility in this pandemic.

So please, media, think about what it means when you say less accurate

It may be exactly the opposite - and in the case of rapid tests, it is

5/
I think general public may not be familiar with term "Specific" in terms of testing

For tests to identify infectious ppl, "Specific" means the test will only be positive when someone is currently infectious (not after). Rapid tests are "Specific" for this. lab PCR not so.

6/

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More from @michaelmina_lab

19 Sep
@MarkZlochin @CircusPubes @DrPathHero1 yes.

A very important piece is the temporal relationship between when viral RNA is highest, when antigen tests are highest sensitivity and when people are most likely to be infectious following exposure. While almost no studies directly observe all three together...
1/
@MarkZlochin @CircusPubes @DrPathHero1 They all fall directly in line with the exact same time period after exposure or - when symptoms are demonstrated, with the same period surrounding onset of symptoms.

So we really do not need empirical data showing transmission and viral load since the kinetics show it all

2/
@MarkZlochin @CircusPubes @DrPathHero1 A major problem obtaining the direct empirical data is that if someone is testing, they likely aren't infecting others. So, people who are infecting others, you simply are not getting their swab at the same time as they are infecting. So relationships are skewed.
Read 5 tweets
17 Sep
To battle COVID, Biden's Action Plan boldy calls for scaling rapid tests! & requires millions of Americans to vaccinate or test

But now the timer is set. W/out immediate change, we will see PCR delays of 3-10 days & rapid test shelves remain largely empty

We can avoid this.
1/
Luckily, the issue is a simple one to fix (all things considered).

The tests exist in HUGE numbers across the globe. Just not in the US. The reason? We've asked the FDA to take on an impossible task... to evaluate high quality PUBLIC HEALTH tools, when this is not their job

2/
The FDA evaluates medical devices - and does not evaluate public health tools

This is THE problem. As long as we consider rapid tests as medical devices (they're not - they're PUBLIC HEALTH transmission detection tools) FDA is forced to fit a square peg in a round hole

3/
Read 8 tweets
16 Sep
DILEMMA

Its common to say ALL kids mask during school, w out mention of daily rapid tests for entry

Yet, it’s heresy to suggest ALL kids test daily and go maskless

- Poor fitting Masks cut transmission, maybe <50%

- Rapid tests cut risk of infectious entering by >90%
I’m NOT suggesting we not do both. But dilemma is:

Why is it that when masks are discussed, rapid tests in AM are not. BUT when rapid tests in AM are discussed, it has to always be followed by “And masks too”.

Demonstrates group think rather than science backed decisions

2/
We DO need rapid test supply. Many ways to make it happen. Change of how they are designated (as a public health tool) is first step in my view so that we can massively accelerate access and scale

Read 5 tweets
15 Sep
Rapid tests work very well to answer 🧵
AM I INFECTIOUS and a RISK TO OTHERS

This is THE public health ? we care about

I made a BIG chart of rapid tests

- Overall sensitivity vs any PCR pos - what FDA judges

- Sensitivity if infectious (97%!) - what we actually care about

1/ Image
This data above comes from the UK COVID-19 Lateral Flow Oversight Team.

What the data above shows is that rapid tests are excellent public health tools to quickly identify almost anyone who is currently infectious and needs to isolate

What it also shows is...
2/
This shows why there is so much damn confusion about if rapid tests are sensitive

Answer: YES they are... if the question is "Am I Infectious Now and do I need to isolate"

However, if we compare them to PCR, then we are asking a different question: Do I have any RNA in me

3/
Read 13 tweets
11 Sep
Notes on sensitivity of rapid Ag tests for what matters: detecting infectious ppl

Sensitivity:

- Highly infectious (ie superspreader levels): >99%

- Moderately infectious (ie infect 2 or 3 ppl in a classroom): 90-95%

- Mildly infectious (ie spread to spouse only) ~80-90%

1/
This Graph of viral load over time helps to explain this sensitivity issue: Image
Further, symptoms vs no symptoms has no impact on test performance. Studies that say it does are not recognizing the sampling bias that enters their studies.

3/
Read 5 tweets
9 Sep
This is tremendously good news! (Thread)

@POTUS fully supporting scale up of rapid at-home tests

I've been arguing for this - the Defense Productions Act to be invoked since early last year to drive production of rapid tests

Testing in a pandemic is a Public Health need

1/
While I am tremendously happy to hear the President say this.

I do have my reservations:

Time is of the essence. If we start the scaling process now, it will take a long time.

Meanwhile many many tests exist globally. We could be using those for the time being.

2/
Importantly, I worry that the 280 million tests that are going to be purchased and produced with the use of the DPA... well, that's less than one test per person over the course of a year. The number sounds big but we do have 330 million ppl in US.

But it is a great start!

3/
Read 10 tweets

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