5 ms·

>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

by Exmoor 7y ago

>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 results on the street in about 10 minutes. This is the only recent testing I've seen that appears to be anything remotely resembling random. The sample size is also not incredibly small. That said, this is the first I've heard that there's a handheld device which can deliver an antibody test in 10 minutes and being completely out of that industry I have to wonder how likely it is that it's delivering a high level of false-positives?

majormajor 7y ago
This doesn't seem that random - it is sampling from people on the street. So it's going to miss people who aren't going out onto the street. And people who are going out are more likely to catch something than those who aren't.
- Exmoor 7y ago
  The previous tests I'd seen (I hadn't read about the Los Angeles test results posted today yet) had been fairly extremely not random. For example the homeless shelter in Massachusetts and pregnant women in New York. That's why I used the phrase "remotely resembling random."
epmaybe 7y ago
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/covid-19-rt/ https://www.biomedomics.com/products/infectious-disease/covi...
- deleted 7y ago
  [deleted]
- skybrian 7y ago
  Specificity of 90% seems really low? Does that mean almost 1 in 10 would test positive even if nobody had it?
  - DenisM 7y ago
    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.
    - subroutine 7y ago
      Or you could flip that around and make testing so plentiful everyone is tested 3x (perhaps by independent labs), so the FP rate is more like... 1/10 * 1/10 * 1/10 (1/1000)
      - notforever 7y ago
        No good reason for test errors to be uncorrelated, ie. quite possible same people who trigger false positives on the first test would be false positives on the second etc.
        subroutine 7y ago
        Sure, there will probably be some correlation. Depends heavily on how the 3x testing is designed. T1. Drive up saliva swab by nurse, for serology test. T2. Re-deploy census peeps to get samples (and census info) from entire neighborhoods. T3. 23andMe-like home kit express mail to lab The odds of people getting a FP on all three might not be 1 in 1000, but it probably isn't 1 in 10. Anyway, as it is, leading 1 in 10 people to falsely believe they are immune, isn't much better than having no test at all.
      - zucker42 7y ago
DeonPenny 7y ago
It has shown to have a 2% false positive rate lower than the 10-15% false positive rate of the general test so its the most accurate test we have. https://abc7news.com/coronavirus-test-free-testing-update-accuracy/6053940/ https://abc7news.com/coronavirus-test-free-testing-update-ac...

by Exmoor 7y ago

majormajor 7y ago

This doesn't seem that random - it is sampling from people on the street. So it's going to miss people who aren't going out onto the street. And people who are going out are more likely to catch something than those who aren't.

Exmoor 7y ago
The previous tests I'd seen (I hadn't read about the Los Angeles test results posted today yet) had been fairly extremely not random. For example the homeless shelter in Massachusetts and pregnant women in New York. That's why I used the phrase "remotely resembling random."

epmaybe 7y ago

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/covid-19-rt/ https://www.biomedomics.com/products/infectious-disease/covi...

deleted 7y ago
[deleted]
skybrian 7y ago
Specificity of 90% seems really low? Does that mean almost 1 in 10 would test positive even if nobody had it?
- DenisM 7y ago
  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.
  - subroutine 7y ago
    Or you could flip that around and make testing so plentiful everyone is tested 3x (perhaps by independent labs), so the FP rate is more like... 1/10 * 1/10 * 1/10 (1/1000)
    - notforever 7y ago
      No good reason for test errors to be uncorrelated, ie. quite possible same people who trigger false positives on the first test would be false positives on the second etc.
      - subroutine 7y ago
        Sure, there will probably be some correlation. Depends heavily on how the 3x testing is designed. T1. Drive up saliva swab by nurse, for serology test. T2. Re-deploy census peeps to get samples (and census info) from entire neighborhoods. T3. 23andMe-like home kit express mail to lab The odds of people getting a FP on all three might not be 1 in 1000, but it probably isn't 1 in 10. Anyway, as it is, leading 1 in 10 people to falsely believe they are immune, isn't much better than having no test at all.
    - zucker42 7y ago

DeonPenny 7y ago

It has shown to have a 2% false positive rate lower than the 10-15% false positive rate of the general test so its the most accurate test we have. https://abc7news.com/coronavirus-test-free-testing-update-accuracy/6053940/ https://abc7news.com/coronavirus-test-free-testing-update-ac...