Covid-19 Antibody Seroprevalence in Santa Clara County, California • Hacker News Board

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

#11

Post by zaroth » Fri, Apr 17, 2020, 4:29 PM UTC

makomk wrote: post #6

vikramkr wrote: post #2

That is certainly alarming that it is so much more widespread than expected - it really highlights the failure of our controls against the virus and the importance of early testing. It I'd good news that this implies the death rate is less severe. However, a caveat is that antibody tests might have high rates of false positives, which would be a particularly large problem when very few people are actually positive. S…

Most signs so far suggest that the virus is basically uncontainable, short of everyone on the planet taking aggressive measures to stop it escaping China back in January or December.

That was back when China was claiming it didn’t transmit between humans, and ordering labs to destroy their samples.

https://www.nationalreview.com/the-morning-jolt/chinas-devas...

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

#12

Post by greedo » Fri, Apr 17, 2020, 4:30 PM UTC

pwned1 wrote: post #5

h2odragon wrote: post #3

I think the numbers will coma out to show this ripped through the USA in February; we slammed the barn doors closed well after the horse was gone. Of course that's not the narrative that fits agendas so just like with "why cant we test people?" back then, there will be many official reasons not to look for antibody data and to doubt what data gets gathered.

Based on the difference between CA and NY, I'd be willing to bet that it got here earlier, maybe in December.

You would have seen more reports in hospitals of interstitial pneumonia, as well as a higher YoY death rate during January.

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

#13

Post by CubsFan1060 » Fri, Apr 17, 2020, 4:31 PM UTC

DennisP wrote: post #9

The problem with every one of these studies I've seen is that they come up with around 3% of the population having antibodies, while a typical false-positive rate for these tests is also around 3%. In this case they claim they adjust for the specificity (basically false-positive rate), but I didn't see that they reported what the specificity was. If the mortality really is very low, then it should be easy to prove. J…

This is certainly not a study. And certainly shouldn't be taken as good data of any kind, but it is interesting: https://www.livescience.com/coronavirus-in-pregnant-woman-hi...

Sure as hell isn't random (all pregnant women... so all women for one. All at the same hospital is another).

"Between March 22 and April 4, those hospitals screened 215 pregnant women for SARS-CoV-2 (the virus that causes COVID-19), and 33 women, or 15%, tested positive. Of these who tested positive, 29 women — or nearly 14% — showed no symptoms."

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

#14

Post by sxp » Fri, Apr 17, 2020, 4:32 PM UTC

There are similar high infection rates from other semi-randomized samples.

https://www.nejm.org/doi/full/10.1056/NEJMc2009316

> Between March 22 and April 4, 2020, a total of 215 pregnant women delivered infants at the New York–Presbyterian Allen Hospital and Columbia University Irving Medical Center . All the women were screened on admission for symptoms of Covid-19. Four women (1.9%) had fever or other symptoms of Covid-19 on admission, and all 4 women tested positive for SARS-CoV-2 (Figure 1). Of the 211 women without symptoms, all were afebrile on admission. Nasopharyngeal swabs were obtained from 210 of the 211 women (99.5%) who did not have symptoms of Covid-19; of these women, 29 (13.7%) were positive for SARS-CoV-2. Thus, 29 of the 33 patients who were positive for SARS-CoV-2 at admission (87.9%) had no symptoms of Covid-19 at presentation.

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

#15

Post by tshadley » Fri, Apr 17, 2020, 4:33 PM UTC

vikramkr wrote: post #2

That is certainly alarming that it is so much more widespread than expected - it really highlights the failure of our controls against the virus and the importance of early testing. It I'd good news that this implies the death rate is less severe. However, a caveat is that antibody tests might have high rates of false positives, which would be a particularly large problem when very few people are actually positive. S…

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

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

#16

Post by fspeech » Fri, Apr 17, 2020, 4:34 PM UTC

There could be a meaningful distinction between exposure and infection. I would define the first as anyone who was exposed to the virus (or even just parts of the virus) and generated antibodies. The second would be an actual infection and presumably a sufficient antibody response to repel the virus and confer immunity to another infection. Really you can generate antibodies without even getting exposed to live virus, just like you can develop allergy to pollen or other foreign objects that enter your body. I would say only the second case is meaningful for public health. For that you need to look at how people do convalescent plasma. You need to test for specific antibodies that actually confer immunity.

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

#17

Post by mgreg » Fri, Apr 17, 2020, 4:34 PM UTC

There's also some data coming out of Wuhan around antibody testing. The methodology is not as well formed as the study in the OP but there is still value in the data.

> Wuhan’s Zhongnan Hospital found that 2.4% of its employees and 2% to 3% of recent patients and other visitors, including people tested before returning to work, had developed antibodies, according to senior doctors there.

Additional antibody testing is also underway in Wuhan.

Source: https://www.wsj.com/articles/wuhan-starts-testing-to-determi...

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

#18

Post by gryson » Fri, Apr 17, 2020, 4:35 PM UTC

"We recruited participants by placing targeted advertisements on Facebook aimed at residents of Santa Clara County..."

I wonder if these ads mentioned the purpose of the study, or if that information was only given out after initial contact (I don't know enough about IRB requirements here).

A concern is that this could cause a selection bias for people who suspected they had the virus. People may respond to such an ad out of curiosity ("I think I had the virus, so it would be good to know for sure") or obligation ("I'm pretty sure I had the virus, so I should help out with this study").

It wouldn't have to be a large selection bias, either. Of the 3,330 people they tested, they found only 50 who tested positive.

I would like to see a bit of a better method of sample selection before drawing any conclusions.

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

#19

Post by standardUser » Fri, Apr 17, 2020, 4:35 PM UTC

Add this to growing pile of evidence that this coronavirus is more widespread than most testing to date would suggest. How much more widespread still appears very unclear. There is a major ramping up of antibody testing happening right now, and multiple new tests being introduced, so we should have a better idea very soon.

But the takeaway should be that this is a good thing. Every unknown case we uncover decreases the overall rate of hospitalization and death, and potentially decreases the effective transmission rate (assuming most people who had the virus develop immunity and that the immunity lasts, which is also still unclear).

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

#20

Post by tgb » Fri, Apr 17, 2020, 4:36 PM UTC

I made this comment the last time a serological testing study came out: they have 30 negative controls and claim 1.5% positives among their tests. So the number of controls is insufficient to rule out this being entirely false positives. You have to then rely on the test manufacturer's claims of false positives rates, which comes from 371 negative controls. They say:

> our estimates of specificity are 99.5% (95 CI 98.1-99.9%) and 100% (95 CI 90.5-100%)

Look at the those confidence intervals, even the narrower one (from the manufacturer's data)! The bottom is a four-fold increase in false positives, compared to the point-estimate, and is greater than the total positives they had in their finding.