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Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

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Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#21

Post by epmaybe »

Exmoor wrote: post #10

>Nearly one third of 200 Chelsea residents who gave a drop of blood to researchers on the street this week tested positive for antibodies linked to COVID-19, a startling indication of how widespread infections have been in the densely populated city. >The doctors used a diagnostic device made by BioMedomics, of Morrisville, N.C., to analyze drops of blood. It resembled an over-the-counter pregnancy test and generated…

Because you quoted the article using BioMedomics' antibody diagnostic test, I will quote the accuracy from their site[0]:

> In order to test the detection sensitivity and specificity of the COVID-19 IgG-IgM combined antibody test, blood samples were collected from COVID-19 patients from multiple hospitals and Chinese CDC laboratories. The tests were done separately at each site. A total of 525 cases were tested: 397 (positive) clinically confirmed (including PCR test) SARS-CoV-2-infected patients and 128 non- SARS-CoV-2-infected patients (128 negative). The testing results of vein blood without viral inactivation were summarized in the Table 1. Of the 397 blood sample from SARS-CoV-2-infected patients, 352 tested positive, resulting in a sensitivity of 88.66%. Twelve of the blood samples from the 128 non-SARS-CoV-2 infection patients tested positive, generating a specificity of 90.63%.

[0]: https://www.biomedomics.com/products/infectious-disease/covi...

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#22

Post by ssivark »

Does this account for the rate of false positives, compounded by the low base rate of disease incidence? When designing such binary estimators, we have a trade off between precision & recall. If the virus affects 1% of the population, and we have a 5% rate of false positives, and close to 100% recall, then ~85% (5:1 odds) of tested positives would be spurious.

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#23

Post by [deleted] »

epmaybe wrote: post #21
Exmoor wrote: post #10

>Nearly one third of 200 Chelsea residents who gave a drop of blood to researchers on the street this week tested positive for antibodies linked to COVID-19, a startling indication of how widespread infections have been in the densely populated city. >The doctors used a diagnostic device made by BioMedomics, of Morrisville, N.C., to analyze drops of blood. It resembled an over-the-counter pregnancy test and generated…

Because you quoted the article using BioMedomics' antibody diagnostic test, I will quote the accuracy from their site[0]: > In order to test the detection sensitivity and specificity of the COVID-19 IgG-IgM combined antibody test, blood samples were collected from COVID-19 patients from multiple hospitals and Chinese CDC laboratories. The tests were done separately at each site. A total of 525 cases were tested: 397…

[deleted]

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#24

Post by skybrian »

epmaybe wrote: post #21
Exmoor wrote: post #10

>Nearly one third of 200 Chelsea residents who gave a drop of blood to researchers on the street this week tested positive for antibodies linked to COVID-19, a startling indication of how widespread infections have been in the densely populated city. >The doctors used a diagnostic device made by BioMedomics, of Morrisville, N.C., to analyze drops of blood. It resembled an over-the-counter pregnancy test and generated…

Because you quoted the article using BioMedomics' antibody diagnostic test, I will quote the accuracy from their site[0]: > In order to test the detection sensitivity and specificity of the COVID-19 IgG-IgM combined antibody test, blood samples were collected from COVID-19 patients from multiple hospitals and Chinese CDC laboratories. The tests were done separately at each site. A total of 525 cases were tested: 397…

Specificity of 90% seems really low? Does that mean almost 1 in 10 would test positive even if nobody had it?

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#25

Post by fortran77 »

wtvanhest wrote: post #11

This is another irresponsible headline. I cannot read the article, so correct me if I am wrong, but if what others said is true... It was not random because they didn't randomly select people, they let people self-select! If they gave the total number of people who took the test, and total number of people asked, you could at least get a range. Of course, that range would still be biased to people who are walking aro…

This is a strong response from someone who claims not to have read the article.

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#26

Post by hinkley »

bitcurious wrote: post #19
jwegan wrote: post #12

Earlier quoted context omitted.

Also biased because they are sampling people who are out and about. People who are out and about likely come into contact with more people than people who are staying at home and rarely going out.

Out, about, and willing to speak to a stranger, which I think is the biggest bias. Pretty much everyone I know goes on the occasional walk, but we all stay the fuck away from other people.

My Hollywood movie plot theory is that Covid affects inhibitions.

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#28

Post by DenisM »

skybrian wrote: post #24
epmaybe wrote: post #21

Earlier quoted context omitted.

Because you quoted the article using BioMedomics' antibody diagnostic test, I will quote the accuracy from their site[0]: > In order to test the detection sensitivity and specificity of the COVID-19 IgG-IgM combined antibody test, blood samples were collected from COVID-19 patients from multiple hospitals and Chinese CDC laboratories. The tests were done separately at each site. A total of 525 cases were tested: 397…

Specificity of 90% seems really low? Does that mean almost 1 in 10 would test positive even if nobody had it?

Yes, it's 10% false positive. But it's not "really low" in the sense that it's typical for antibody tests. Which is one reason not to do wide-spread testing.

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#29

Post by michaeloder »

epmaybe wrote: post #21
Exmoor wrote: post #10

>Nearly one third of 200 Chelsea residents who gave a drop of blood to researchers on the street this week tested positive for antibodies linked to COVID-19, a startling indication of how widespread infections have been in the densely populated city. >The doctors used a diagnostic device made by BioMedomics, of Morrisville, N.C., to analyze drops of blood. It resembled an over-the-counter pregnancy test and generated…

Because you quoted the article using BioMedomics' antibody diagnostic test, I will quote the accuracy from their site[0]: > In order to test the detection sensitivity and specificity of the COVID-19 IgG-IgM combined antibody test, blood samples were collected from COVID-19 patients from multiple hospitals and Chinese CDC laboratories. The tests were done separately at each site. A total of 525 cases were tested: 397…

A 10% false-positive rate is awful. If the actual incidence is 2%, a test with that error rate could overstate the results at about 12%. That combined with the sampling bias could easily result in overstated numbers.

Randomized household sampling would be far preferable. That would obviously take much more time and would expose testers and the household to more risk. But without good methods, research like this and the surveys conducted in Santa Clara and LA counties are potentially worst than useless since they have the potential of misinforming policymakers and the public.

Re: Nearly a third of blood samples taken in Chelsea show exposure to coronavirus

#30

Post by DeonPenny »

acchow wrote: post #27

Can we change the title? Article title is "Nearly a third of 200 blood samples taken in Chelsea show exposure to coronavirus" The sample is clearly not random

Your never going to have a completely random test. Your randomness comes from you picking for an area and the people who chose to do the test. Saying otherwise is being pedantic to your detriment.
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