
U.S. Navy test shows 60 percent of carrier crew have coronavirus antibodies - throwaway888abc
https://www.reuters.com/article/us-health-coronavirus-usa-navy-exclusive/exclusive-u-s-navy-test-shows-60-percent-of-carrier-crew-have-coronavirus-antibodies-idUSKBN23F29Z
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Press2forEN
In a previous report by Reuters, all 4,800 personnel were tested for COVID-19.
600 tested positive of which 360 were symptom-free leaving 240 that tested
positive and showed symptoms. 1 person died [1].

This report indicates that of a sample of 400 volunteers that agreed to take
an antibody test, 240 tested positive and 160 did not. It also indicates that
1,100 people tested positive for COVID-19 back in April, possibly an update to
the first report of 600.

At this point it appears that in this mini-testing lab of an aircraft carrier,
about 25% of the crew tested positive for COVID-19 and 60% tested positive for
antibodies, which seems to match with the earlier results showing that 60% of
the sailors were symptom-free.

[1] - [https://www.reuters.com/article/us-health-coronavirus-usa-
mi...](https://www.reuters.com/article/us-health-coronavirus-usa-military-
sympt/coronavirus-clue-most-cases-aboard-u-s-aircraft-carrier-are-symptom-
free-idUSKCN21Y2GB)

~~~
ars
I wish they would correlate the two datasets: Of those who tested positive how
many also had antibodies.

This would answer the question on if antibodies are a valid way to check for
prior exposure.

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aazaa
> The officials, speaking on the condition of anonymity, said that about 400
> volunteers participated in the serology tests, lower than the 1,000
> volunteers that were sought, but enough to provide statistically relevant
> data about how the virus spread aboard one of world’s largest warships.

There could be a correlation between the probability of getting tested and the
probability of having had COVID-19-like symptoms or known exposure. In this
sense, the Navy study resembles the ones that sampled from willing shoppers in
front of grocery stores. Drawing conclusions isn't very easy here.

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avsteele
This probably under counts the true number of infection significantly.

If the sensitivity/specificity of the test was similar to the paper below,
true prevalence for the ship probably approaches 100%.

[https://www.biorxiv.org/content/10.1101/2020.05.13.092619v2](https://www.biorxiv.org/content/10.1101/2020.05.13.092619v2)

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JumpCrisscross
> _This probably under counts the true number of infection significantly_

Probably not. Ships are unusually concentrated social environments.

~~~
algorithmsRcool
I don't understand, wouldn't a concentrated social environment suggest very
high infection rates, which aligns with the GP?

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guscost
It's not just infection rates, it's also dose/severity. See my linked paper.

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thephyber
This was a sample not a full test of all sailors on the ship and it was based
on serology tests as developed by April.

> about 400 volunteers participated in the serology tests

> The Roosevelt has about 4,800 personnel on the ship.

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throwaway894345
This sample is statistically significant. Not sure what the problem is?

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beervirus
It’s not a random sample.

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JPKab
In the sense that they requested 1,000 volunteers, and 400 signed up? Do you
mean it's a selection bias due to only a certain kind of person who signs up
for these things getting tested?

~~~
ipsum2
People would sign up if they suspected they had coronavirus based off of their
symptoms.

~~~
thephyber
This comment thread is about antibodies.

There was a different line of testing for who actually had the active
virus/disease which included far more sailors from the ship:

> As of Monday, the Navy had tested 94 percent of the crew for the virus, with
> 678 positive and 3,904 negative results.

[1] [https://www.politico.com/news/2020/04/21/navy-extends-
isolat...](https://www.politico.com/news/2020/04/21/navy-extends-isolation-
for-uss-theodore-roosevelt-sailors-may-delay-ship-departure-198081)

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PeterStuer
This was not a random sample, with reasonable probability of a selection very
skewed towards those suspecting a higher infection risk.

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mywittyname
I'm surprised that it's not much higher. I would have expected over 90%.

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baxtr
I know a person who had mild symptoms, was tested positive in the PCR test and
did not have any antibodies 6-8 weeks later. He then looked into the subject
deeply. His conclusion was: You _can_ develop antibodies after infections, but
not everybody does. Also: a lack of ABs does not mean that you aren't immune.
After all, many people were asymptomatic or showed only mild symptoms without
any ABs... There is the second, much less known immune system called cellular
response, which seems to play a strong role in this disease.

~~~
KCUOJJQJ
Isn't it also possible that the PCR test was wrong and it was something else,
like a cold?

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baxtr
As far as I know a false positive in PCR is not very likely, but of course it
is possible.

~~~
T-hawk
PCR is very unlikely to give a false positive if you never had the virus. The
viral RNA simply isn't present to be detected. A false positive from PCR most
likely came from contamination of the test materials.

PCR is quite likely to give a false positive _if you previously had the virus
but have recovered_ , including asymptomatic cases. There are still pieces of
viral RNA that can be detected by PCR, even if they're inactivated by having
destroyed the viral coating and you're no longer contagious.

So PCR is pretty accurate at saying _if you ever had the virus_ , but not so
accurate at saying if you _currently_ have it at contagious levels.

