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

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

#121

Post by taeric » Fri, Apr 17, 2020, 7:14 PM UTC

tmandry wrote: post #94

all_usernames wrote: post #86

Earlier quoted context omitted.

It's known that the vast majority infected do not experience symptoms, or have mild symptoms. I don't think you can draw the conclusion that they had prior immunity.

“mild” symptoms has been used to mean flu-like, i.e., not something I would call mild and certainly not the same as asympotomatic, but not requiring hospitalization.

I think it is stranger than that. Mild has been anything from a fever for a night, to flu like for a week or so.

Really want to get a test on myself and family. We had something that near hospitalized me, but the kids barely registered being sick.

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

#122

Post by taeric » Fri, Apr 17, 2020, 7:16 PM UTC

usaar333 wrote: post #110

robotcookies wrote: post #104

"Participants were recruited using Facebook ads targeting a representative sample of the county by demographic and geographic characteristics." How is it representative when it's only Facebook users in this sample?

Unless you think FB users for some reason would be infected at significantly different rates, that shouldn't be much of a problem. I'm much more concerned about selection bias toward prior sick people; IIRC, Stanford offered to report positive results to the patient.

Unless nursing homes are represented well in Facebook, I'd wager the bias is against what we believe to be the biggest risk pool.

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

#123

Post by jhayward » Fri, Apr 17, 2020, 7:24 PM UTC

microdrum wrote: post #40

This is very strong evidence that the "realists" like Alex Berensen were correct. The shutdowns probably should end, while encouraging at-risk populations (mostly retired) to stay at home.

Data from Wuhan was that in the early phase of the epidemic about 70% of infections were transmitted at home. Once they realized this, they went to rapid isolation of positive tests and quarantine of contacts in “COVID hotels” away from home.

So your suggestion is entirely unworkable unless there is a plan to remove all at-risk persons from contact with low-risk persons.

Please show your work and let us know what that plan looks like. Who will care for these people, how will they be housed, how will you prevent the care force from bringing infection to them ala nursing homes, etc.

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

#124

Post by tom-thistime » Fri, Apr 17, 2020, 7:30 PM UTC

crdrost wrote: post #111

tom-thistime wrote: post #96

Earlier quoted context omitted.

Most of what I've seen suggests that at time of positive test results, 40% to 70% of people have not experienced symptoms. Have you seen numbers very different from that? [Edit: 'No symptoms experienced at time of positive test results' is intended to mean the same as 'no symptoms experienced yet at time of positive test results'.]

That can't be true for the official confirmed numbers. Like, it was for a while impossible to get a test if you are not experiencing multiple symptoms AND can make a case that you might have been exposed via interacting with someone who has traveled. Even now I don't think they're giving the test if you don't have a fever. It's implausible that 50% of the people tested by the official pathway had no symptoms because…

Ok, we can't conclude anything about the rate of symptoms from testing that was only conducted on people showing severe symptoms. I don't think we can conclude much of anything from the OP either, because its rate of positives seems compatible with the rate of false positives from the test. They could have 0% infected, they could have 5% infected.

An example where testing was conducted without requiring symptoms first: https://taskandpurpose.com/news/uss-theodore-roosevelt-sailo...

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

#125

Post by guscost » Fri, Apr 17, 2020, 7:35 PM UTC

fspeech wrote: post #34

makomk wrote: post #6

Earlier quoted context omitted.

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.

How do you square that with the fact that there is no outbreak in any overseas Chinese community? Not Taiwan or Hongkong or Macau, nor in the epicenter of Italy ( https://www.reuters.com/article/us-health-coronavirus-italy-... ), nor San Francisco Chinatown ( https://www.nytimes.com/2020/04/17/us/san-francisco-coronavi... )? All of these communities have far more ties to mainland China.

It could have already passed through all of those communities basically unnoticed, and/or confused with other ILIs. There's no way to rule out that possibility, and when you consider how rare cardiovascular diseases (the most common comorbidity) are in those communities, you have to conclude that it's not vanishingly unlikely: https://minorityhealth.hhs.gov/omh/browse.aspx?lvl=4&lvlid=4...

Obviously mitigation efforts still play some part in limiting the spread, but I would not bet that all of those communities were able to suppress such a contagious disease before a big chunk of the population was exposed to it.

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

#126

Post by jhayward » Fri, Apr 17, 2020, 7:39 PM UTC

vl wrote: post #119

tomerico wrote: post #93

Saw this comment [1] on Reddit that outlines the limitations of the study well: This is the most poorly-designed serosurvey we've seen yet, frankly. It advertised on Facebook asking for people who wanted antibody testing. This has an enormous potential effect on the sample - I'm so much more likely to take the time to get tested if I think it will benefit me, and It's most likely to benefit me if I'm more likely to h…

It’s better to have data and know its limitations, than not to have data at all.

This may be a true statement when applied to public health professionals, but is quite likely dangerous to public welfare when in the hands of disinformation campaigns and propaganda.

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

#127

Post by wool_gather » Fri, Apr 17, 2020, 7:46 PM UTC

tom-thistime wrote: post #124

crdrost wrote: post #111

Earlier quoted context omitted.

That can't be true for the official confirmed numbers. Like, it was for a while impossible to get a test if you are not experiencing multiple symptoms AND can make a case that you might have been exposed via interacting with someone who has traveled. Even now I don't think they're giving the test if you don't have a fever. It's implausible that 50% of the people tested by the official pathway had no symptoms because…

Ok, we can't conclude anything about the rate of symptoms from testing that was only conducted on people showing severe symptoms. I don't think we can conclude much of anything from the OP either, because its rate of positives seems compatible with the rate of false positives from the test. They could have 0% infected, they could have 5% infected. An example where testing was conducted without requiring symptoms firs…

Yes, although note that it's not clear which kind of test is being used by the Navy there.

If it's the nasal swab-PCR test that most civilians are getting, then the claim of "asymptomatic" must be accompanied by a "yet". We can't really conclude anything for at least two weeks after the positive result -- after seeing whether those people ever develop symptoms.

If it's blood-antibody testing, then we can give the statement a little more weight, because a positive result would mean the infection is in a later stage or even past. I have no idea whether the Navy is using these tests.

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

#128

Post by jhwang5 » Fri, Apr 17, 2020, 7:46 PM UTC

terramars wrote: post #71

my friend probably had the virus (2 inconclusive tests) and tried to get into this study. some group asked her for $125 to get tested. i'm not sure if she saw any of the facebook ads. so, grain of salt about representativeness of the sample. there's for sure a response bias towards people who think they had it.

Just curious, did your friend have pretty severe symptoms? As in, was it worse perceivably than say a case of bad flu?

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

#129

Post by Medicalidiot » Fri, Apr 17, 2020, 7:47 PM UTC

jacquesm wrote: post #101

Medicalidiot wrote: post #80

Antibody tests are not as accurate as RT-PCR, but the sensitivity that was observed here was 91% and 99% specificity when compared to confirmed COVID cases. I just want to point out that these researchers are using the corrects tests to do this.

They use the correct tests, but they use them on a group that isn't even close to a random sample of the population, which is what you'd need to do to get to their conclusion.

I'm not going to comment on that because I have a basic understanding of public health and epidemiology on the diagnostic side of things. Why do you think that this isn't a "good" random sample?

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

#130

Post by joe_the_user » Fri, Apr 17, 2020, 7:47 PM UTC

MiguelVieira wrote: post #109

erentz wrote: post #79

It’s hacky and I’m happy to be told how wrong it is. But based on these recent antibody studies in Germany, Finland, and now here in CA, I’ve been assuming an actual fatality rate of about 0.4, and thus an actual infected rate of 250x our known deaths, which is a much firmer number. This is only a small comfort since it means we may have had about 8.75 million infected and presumably now immune in the USA. Or about 2…

I've been using 0.5% for mental math, rounding down from the lower bound from this study in The Lancet: https://www.thelancet.com/journals/laninf/article/PIIS1473-3... I would be surprised if, after this current wave of infections, the percentage of people with antibodies in the US is higher than the low single digits. Herd immunity without a vaccine is a pipe dream. Our best bet is to massively ramp up testing and c…

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 and awful but it seems like with the current administration approach, the response of ramped up contract tracing has pretty much flown away and with these figures, we're looking 500K deaths, 250K over the next two month and another 250K over a longer period. Hide your parents...