Thread by @gbosslet

There is chatter about this study in @nature that "disproves" asymptomatic spread- ergo, lockdowns were unneeded.

Let's unpack this because I think this is a blatant misinterpretation of this amazing study.

go.nature.com/3rAmzgV

1/

First off, let's talk about what an unbelievable study this is.

The city of Wuhan, China had a SARS-CoV-2 screening program in which they set out to test all city residents- and were successful in testing 9,899,828 individuals (92.9% of eligible citizens).

IN 19 DAYS.

2/

Wuhan has the equivalent population to North Carolina.

As of today, North Carolina has only carried out 6,800,055 tests (and this is not individuals- this includes multiples).

Wuhan did in 19 days what North Carolina has not done in 10 months.

3/

Wuhan PCR tested ~10 million people over 19 days, finding 300 positives in the population.

They contact traced 1174 contacts of these 300 people and ALL WERE NEGATIVE.

Thus the conclusion: asymptomatic spread does not happen.

THIS IS NOT WHAT THIS STUDY IMPLIES.

4/

Wuhan locked down (and I mean LOCKED DOWN to an extent no Americans can imagine) from January 23 to April 8, 2020.

This study was conducted May 14 to June 1, 2020.

So the screening samples were collected 5 weeks after the END of an almost 3-month lockdown.

5/

It is far more likely that THERE WAS SIMPLY NO CIRCULATING LIVE VIRUS IN THE POPULATION during the time of this study.

I would posit that those 300 positives were carrying harmless leftover viral RNA in their noses ("re-positives"), not actual virus that could infect anyone.

6/

This is one of the difficulties of the PCR test- it is sensitive enough that it will pick up plenty of people who have been infected in the past but are simply now carrying viral detritus.

It is, TBH, an achilles heel of the whole testing apparatus.
7/

This hypothesis is supported by the fact that the average cycle threshold (Ct) for these 300 positive tests was around 34, which is near the cutoff for positive testing in many labs (which I think is around 37 in the labs at my shop).

8/

In a different study, PCR Ct values of >35 yielded culturable virus in only 8% of samples.

bit.ly/3rF7E4Y

And more than 20 days after symptoms, 0 of those still PCR positive had culturable virus.

The Wuhan study STARTED 35 days after the lockdown ended.

9/

And studies of people who continue to be PCR positive from South Korea have shown PCR can remain positive for up to three months after infection.

bit.ly/3mYUX1n

Of 285 "re-positive" individuals, Korean CDC traced 790 contacts- no one developed SARS-CoV-2.

10/

This is why @CDCgov guidelines do not suggest "testing for cure" for most people and that isolation cease 10 days after symptom onset or (if asymptomatic) after positive PCR.

bit.ly/3hrvCMe

Because you will find a reasonable number of "re-positives".

11/

Going back to the Wuhan study, the authors' conclusion that "there was no evidence that the identified asymptomatic positive cases were infectious." is technically correct, but is very poorly worded.

12/

It is more appropriate to say "it was unlikely that the identified asymptomatic positive cases carried actual virus."

Because I think it far more likely that they found 300 re-positives. Not asymptomatic infections.

13/

In transparency, the last cases of SARS-CoV-2 in Wuhan were 6 cases identified May 12, 2 days before this screening program began. So it is not as though there was NO virus there for months.

But they were found and isolated and there was no community spread from these.

14/

Concluding from this study that asymptomatic spread doesn't happen is folly. This is far from what this study implies.

Many are using this to claim lockdowns shouldn't happen because this study disproves asymptomatic spread.

It doesn't AT ALL.

https://twitter.com/MihaiVioreanu/status/1330081271213662208?s=20

15/

What this study conclusively demonstrates is that China was able to take Wuhan from somewhere between 50,000 and 500,000 SARS-CoV-2 infections (bloom.bg/3n0rp3x) to ZERO in a matter of months.

16/

And it suggests that 6 weeks after our last case in the U.S., if we tested every American with PCR, around 10,000 would be "re-positives", indicating they are carrying viral detritus, not virus that threatens to bring the pandemic back again.

FIN/