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Nearly a third of blood samples taken in Chelsea show exposure to coronavirus
- rogerkirkness 7y agoIf the R0 is truly near six, we have probably climbed near the top of the S curve already all over the place. We will know in a month.
- neonate 7y agohttp://archive.md/UDrho http://archive.md/UDrho
- point78 7y agoSo halfway to herd immunity?
- downerending 7y agoGo Cows!
- Exmoor 7y agoIt was discussed in another thread that I'll try to dig up, but the percentage of the population required to reach herd immunity goes up the more contagious a virus is. If way more people are infected then we think, then it points to some of the higher R0 estimates being accurate and would therefore require a much higher portion of the population to be immune before we reach herd immunity. Edit: Here it is: https://news.ycombinator.com/item?id=22819057 https://news.ycombinator.com/item?id=22819057
- james_s_tayler 7y agoMy understanding is it's (R0 - 1)/R0 So if R0 is 4 then 3/4 of the population is required to be immune before herd immunity kicks in.
- retsibsi 7y agoYeah, I'm not an epidemiologist but I think the principle is simple: it's just a matter of getting the actual transmission rate below 1, so that any outbreak will naturally die out. If in the absence of any immunity the average infected person infects 3 others, but now 2/3 of people are immune, then the average infected person will actually only infect one other. Ditto for a transmission rate of four and 3/4 immunity, and so on. It's worth noting, though, that the natural tendency during an epidemic is for the total number of infections to exceed the herd immunity threshold; I think the phrase to google is 'herd immunity overshoot'. (It's also worth noting the serious problems with this study, as pointed out by other commenters.)
- Gibbon1 7y ago> herd immunity overshoot I saw that too when mucking with simple models. The percent infected overshoots (R0 - 1)/R0. So that is a threshold for herd immunity not the ultimate infection ratio. They're only equivalent under steady state conditions. Also saw an study released by the CDC that estimated that the initial r0 in Wuhan was 5.8. Explains what happened in Northern Italy and New York. The epidemic achieved break out while most infected were still mildly ill or asymptomatic.
- tanilama 7y ago> The 200 participants generally appeared healthy, but about half told the doctors they had had at least one symptom of COVID-19 in the past four weeks. The total sample size is small and this doesn't seem random enough?
- Hermel 7y agoYou should be much more worried about bias than about sample size. See also this calculation, where it is discussed that a sample of 400 is more reliable than a slightly biased sample of a million participants: https://marginalrevolution.com/marginalrevolution/2020/01/big-datasmall-bias.html https://marginalrevolution.com/marginalrevolution/2020/01/bi...
- scythe 7y agoA third of a random sample taken in Chelsea, Massachusetts: https://en.wikipedia.org/wiki/Chelsea,_Massachusetts https://en.wikipedia.org/wiki/Chelsea,_Massachusetts >Chelsea is [...] directly across the Mystic River from the city of Boston. [...] It is also the second most densely populated city in Massachusetts behind Somerville. A random sample in a highly affected and extremely dense area is not a model for the whole state.
- powvans 7y agoAs soon as I saw this study I Googled Chelsea Mass and in the first few results was an article about how it has been hit hard by the virus. From the article: > “Chelsea is suffering in this pandemic,” City Manager Tom Ambrosino told WBZ News. “We have, as far as I can determine, the highest infection rate in the Commonwealth.” [1] With that information the takeaway should be that in the areas with the highest rate of infection we are seeing as much as 30% of the population with antibodies. That's great and an encouraging statistic that seems to indicate the percentage of mild or asymptomatic cases is much higher than originally believed. It does not mean that we are close to herd immunity everywhere. We need randomized testing in many many more communities across the country in order to get the full picture. [1] https://www.boston.com/news/local-news/2020/04/10/chelsea-massachusetts-coronavirus https://www.boston.com/news/local-news/2020/04/10/chelsea-ma...
- lubujackson 7y agoChelsea is literally the hardest hit town in MA: https://www.nbcboston.com/news/local/the-20-communities-with-the-highest-rate-of-coronavirus-cases-in-mass/2108780/ https://www.nbcboston.com/news/local/the-20-communities-with... I have some natural doubts over all these antibody tests that indicate herd immunity while covering up major flaws...
- ghaff 7y agoFurthermore, a very working class city so I'm sure that a far lower percentage of people are staying home than in many places. [ADDED: Given jobs that don't allow them to stay home.]
- kgwgk 7y ago
- trav4225 7y agoHmm, I wonder if they attempt to control for bias. It sounds as though they were asking random passersby if they wanted a COVID-19 antibody test. If so, it seems that the sample group could be biased toward including more people who suspected that they may have been infected (previously or currently) than a truly random sample.
- jwegan 7y agoAlso 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.
- bitcurious 7y agoOut, 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.
- hinkley 7y agoMy Hollywood movie plot theory is that Covid affects inhibitions.
- youareostriches 7y agoIt’s certainly not a hollywood movie—for the flu, it’s already the case! Change in Human Social Behavior in Response to a Common Vaccine https://pubmed.ncbi.nlm.nih.gov/20816312/ https://pubmed.ncbi.nlm.nih.gov/20816312/ Conclusions: These results show that there is an immediate active behavioral response to infection before the expected onset of symptoms or sickness behavior.
- pmoriarty 7y agoYou might enjoy David Cronenberg's film Rabid.
- 7y ago
- 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 agoThis 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 agoThe 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 agoBecause 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...
- wtvanhest 7y agoThis 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 around during a time when they should be sheltering in place. At best, 30% of people who were offered a covid antibody test in public had antibodies. I think its safe to say that journalists have a responsibility to get the headlines right on this topic or they risk causing a lot of people to make bad decisions after hearing that 30% of people already have this disease. There is a real human cost of this click-bait, and it will be deaths.
- fortran77 7y agoThis is a strong response from someone who claims not to have read the article.
- retsibsi 7y agoIs it wrong, though? I did read the article, and I don't think so. One relevant thing GP may have missed is that the researchers "excluded anyone who had tested positive for the virus in the standard nasal swab test". So they weren't quite trying to directly estimate the proportion of people with antibodies, but the proportion of people without a positive test with antibodies. But I suspect this didn't change the results much: how many people in the area have tested positive and recovered sufficiently to be out in public?
- duxup 7y agoIt would be nice if it was more widespread than we think. Presumably that would mean we would be closer to the end of the tunnel?
- marshalltony 7y agoDon't worry, HN will find something wrong with it. We could test every single person in the US and you guys would find something wrong with it if it showed good news. This place is worse than /coronavirus
- ssivark 7y agoDoes 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.
- acchow 7y agoCan 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
- DeonPenny 7y agoYour 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.
- Retric 7y agoIt’s normal to randomly sample multiple locations. Random samples from even 10 random locations are much more useful.
- umanwizard 7y agoNot really... more data can't fix sampling bias.
- Retric 7y agoIt’s not a question of ‘more data’ as I could take 50 or 50,000 samples from a single person and I gain nothing about the overall population. Similarly if I sample 50 or 50,000 people from a single city I learn nothing about people outside of that city. But, by sampling N random locations I at worst have N samples to work with. PS: At the extreme, if I sample every single member of a population then ‘more data’ solved any bias problems. Smaller samples are subject to a wider range of biases.
- DeonPenny 7y agoNot if you are trying to figure out the best decision for a specific city/state
- umanwizard 7y agoYou can choose to offer people some incentive to take the test. If you offered $50 per person you would probably eliminate most sampling bias.
- ltbarcly3 7y agoThis isn't random at all, lots of people are staying inside and going out to the store once a week or less, they will be dramatically under tested with this methodology. Meanwhile other people are going out every day, or they know they previously had covid so they consider themselves exempt from shelter in place, or they have a job that requires them to continue heading out to work despite shelter in place (and therefore they have had far more exposure to covid than average).
- cameldrv 7y agoHas anyone been able to figure out what the number of COVID deaths are in Chelsea specifically?
- contravariant 7y agoThe article claims 712 detected cases resulting in (at least) 39 deaths. Chelsea has a population of about 40k, this isn't mentioned in the article but matches the article's figure of around 1900 cases per 100,000. Assuming 30% of the population is infected this puts the current number of deaths at around 0.3% of the total infected. There is some bias due to the rate of false positives of the test and the lag in the number of deaths, so the actual fatality rate may well be higher, but the order of magnitude seems consistent with the numbers discussed in previous threads [1]. [1]: https://news.ycombinator.com/item?id=22901311 https://news.ycombinator.com/item?id=22901311
- ScottFree 7y agoDoes anybody how these antibodies are being identified and how distinct they are from other, similar viruses (like the flu)?
- Rantenki 7y agoAlright. So what's the rate of false positives for that test? In other words, if this test (and similarly the stanford study in LA) have even a small rate of false positives, combined with any sampling bias, it's going to lead to some misleading conclusions.
- DougN7 7y agoThis sucks, but also means we’re inching closer to the 70-80% necessary for herd immunity so maybe a silver lining?
- kanzenryu2 7y agoThere have been reports of tests giving up to 30% false positives