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Covid-19 Antibody Seroprevalence in Santa Clara County, California

medrxiv.org

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Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#161

Post by danieltillett »

projektfu wrote: post #38
tshadley wrote: post #15

Earlier quoted context omitted.

Note coauthor name "John Ioannidis". That gives the paper a healthy boost in my view.

Careful, though, because just being a critic doesn't mean he isn't susceptible to the same sorts of biases and issues that cause a lot of other medical papers to fail. I'm hoping he's on the paper because they ran it by him for a thumbs-up before submitting it.

I hope he is not on the paper for that reason as this is basically honorary authorship. If he just reviewed the paper before submission then he should be in the acknowledgements.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#162

Post by JamesBarney »

gryson wrote: post #64
compiler-guy wrote: post #50

Earlier quoted context omitted.

These are very common statistical methods when dealing with surveys and populations. It isn't this paper's job to describe the background on something like that, just like it isn't this papers job to explain blood testing. They describe their limitations and adjustments exactly like most other studies of this sort do. For example: "Those imbalances were partly addressed by weighting our sample population by zip code,…

On the contrary - detecting selection bias of this sort can be very difficult. Do you measure it using a questionnaire? You might ask your subjects "Do you think you previously had COVID-19?" But what do you do with that response data? Exclude everyone that says yes? Then you're skewing one way. There's obviously no population data to match that response with like there is for general demographics such as race and ag…

I think you'd call individuals(using a method with far less self selection bias) and get them to fill out the same questionnaire and then do the same types of adjustments you'd do with race or gender.

But I also agree they 100% did not do any of these adjustments if they did it would be listed right here

> We report the prevalence of antibodies to SARS-CoV-2 in a sample of 3,330 people, adjusting for zip code, sex, and race/ethnicity. We also adjust for test performance characteristics using 3 different estimates: (i) the test manufacturer's data, (ii) a sample of 37 positive and 30 negative controls tested at Stanford, and (iii) a combination of both.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#163

Post by JamesBarney »

irq11 wrote: post #145
joe_the_user wrote: post #130

Earlier quoted context omitted.

So a 0.5% fatality rate sounds like "only" five times the rate of the flu. EXCEPT that I would bet that if you thoroughly traced all the asymptomatic but positive for the flu, it's fatality rate would decline also and it still causes significant deaths. Total Covid deaths are already at a "mild flu season" level already after a month and continuing some level of exponential growth after social distancing. It's sad an…

Except that a huge portion of those deaths are in places that may have already reached herd immunity, if the ratio of comfirmed / actual cases is as small as this study suggests. NYC, for example, has 123k confirmed cases. Multiply by 50, and you have 6.1M, which is close to 70% of the total population.

Where are you getting the assumption that only 1 in 50 infected are confirmed? That seems like an especially low confirmed case to infection ratio.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#164

Post by JamesBarney »

Fjolsvith wrote: post #120
usaar333 wrote: post #63

Earlier quoted context omitted.

NYC has 30x the per capita death rate of Santa Clara county. Santa Clara county only being 15% as infected is not consistent.

What if there are other, undiscovered factors that could explain the difference? Such as NYC populace having had exposure to some other virus that predisposed them to a greater vulnerability. Or perhaps, air pollution exposure predisposing them to greater vulnerability.

We have two possible hypotheses.

There is an unknown quality about New York that causes the virus to be 4 times more severe.

A self-selected group from the internet demonstrated self-selection sampling bias.

I know where I would put my money.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#165

Post by [deleted] »

cameldrv wrote: post #103
cuchoi wrote: post #8

Caveat from the paper: "This study had several limitations. First, our sampling strategy selected for members of Santa Clara County with access to Facebook and a car to attend drive-through testing sites. This resulted in an over-representation of white women between the ages of 19 and 64, and an under-representation of Hispanic and Asian populations, relative to our community. Those imbalances were partly addressed…

Yes, and look at the way they corrected for this. They rebalanced for demographics, and that doubled their estimate. This is exactly the opposite of what they should have done. For example, zip codes farther from the testing sites were less likely to get tested, and more likely to be positive. What you see is that certain groups were less likely to go get tested, UNLESS they had a good reason to think that they were…

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Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#166

Post by cactus2093 »

guenthert wrote: post #136
cameldrv wrote: post #103

Earlier quoted context omitted.

Yes, and look at the way they corrected for this. They rebalanced for demographics, and that doubled their estimate. This is exactly the opposite of what they should have done. For example, zip codes farther from the testing sites were less likely to get tested, and more likely to be positive. What you see is that certain groups were less likely to go get tested, UNLESS they had a good reason to think that they were…

With the average adult getting two bouts of common cold each year and mild COVID symptoms resembling a common cold, I'd think a large fraction of the population might think they had it. I wouldn't dear to guess in which way this shifts the estimate. I think it's understood, that with such a small sample size, results are to be taken cautiously. You have to start somewhere though.

Given that testing is still limited and you have to really make a case for yourself to get it, the group of people who have been tested (not for the antibodies, for infection) is at least a lower bound on the people who think they had it. And statewide we have been at around 12% positives, so it's reasonable to say at least 88% of people who think they had it didn't.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#167

Post by cactus2093 »

notforever wrote: post #156
usaar333 wrote: post #63

Earlier quoted context omitted.

NYC has 30x the per capita death rate of Santa Clara county. Santa Clara county only being 15% as infected is not consistent.

Just a hypothesis, but if being more frequently exposed makes it more likely that the disease will be more severe, then this is plausible. There is some evidence that e.g. doctors/nurses were more likely to die compared to their age cohort, possibly because of higher viral load.

I've definitely seen the opposite stated, that doctors/nurses are not actually more likely to die. I forget if it was Italy or NYC, but the fatality rate for doctors & nurses had been something like 0.5%. They are much more likely to be infected than anyone else, and there has (rightly) been lots written about the doctors and nurses who have died, which gives people this perception.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#168

Post by grandmczeb »

projektfu wrote: post #149
grandmczeb wrote: post #148

Earlier quoted context omitted.

> it seems to have a high rate of hospitalization in clinical cases. The raw hospitalization rate is inflated because both treatment and testing are mostly limited to very severe cases in places where there's a lot of confirmed cases (e.g. NYC.)

Still, comparing it to influenza... we dont see this many severe cases typically.

Its pretty obvious this is worse than the flu. I don't think anyone is really disputing that at this point.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#169

Post by lbeltrame »

yread wrote: post #76
microdrum wrote: post #47

Earlier quoted context omitted.

Yep. You've got nothing. CFR is low, and this has been knowable for a long time. You're scared. It's OK. It's illogical and anti-scientific, but it's OK. But you won't be able to hurt ordinary people any longer. Here's Germany's imputed CFR: https://spectator.us/covid-antibody-test-german-town-shows-1... Here's Denmark: https://www.dr.dk/nyheder/indland/doedelighed-skal-formentli... Here's Iceland: https://reason.com…

Few non-peer reviewed papers with biased samples, questionable tests and questionable methodology don't make strong evidence. CFR just can't be that low. There are towns in Italy where the virus killed 1% of total population https://www.ecodibergamo.it/stories/valle-brembana/il-grido-...

Given that there was a disaster (in the sense of failed containment) in the hospital of Alzano Lombardo early on (which is in the area), I wonder if that meant that more vulnerable segments of the population were exposed to the virus.

Re: Covid-19 Antibody Seroprevalence in Santa Clara County, California

#170

Post by [deleted] »

ysleepy wrote: post #62
microdrum wrote: post #47

Earlier quoted context omitted.

Yep. You've got nothing. CFR is low, and this has been knowable for a long time. You're scared. It's OK. It's illogical and anti-scientific, but it's OK. But you won't be able to hurt ordinary people any longer. Here's Germany's imputed CFR: https://spectator.us/covid-antibody-test-german-town-shows-1... Here's Denmark: https://www.dr.dk/nyheder/indland/doedelighed-skal-formentli... Here's Iceland: https://reason.com…

You are oversimplifying. While these numbers are indicators, they are non-representative samples. Different communities spread the disease to different demographics. A CFR of 0.4% is still huge, especially if it is very non-uniform and would mean 1.2mio deaths in the US if it saturates. And if that isnt enough for you, we still don't have reliable information about long term effects of an infection. It could end up b…

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