Pedestrian |
May 16, 2020 11:16 PM |
Quote:
Originally Posted by CaliNative
(Post 8924346)
Doc--What percentage of the population do you suspect have had or have the disease? Some estimates are maybe 5% or more in many areas (Bay area, maybe not--NYC, maybe). Assymptematic cases rarely get tested so we don't know. At what % does "herd immunity" start to reduce infections significantly--over 50% of pop?. Any tips on getting good surgical masks or even better N95s? Scary to go out & shop without a good mask. Of course the medical professionals should get the first crack at them, but older people should too Can masks from China be trusted? So many reports of flaws in them in the media. What is your opinion on when the national number of cases subsides--later this month? Looks like remdesivir helps but is in short supply.
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I really have no idea and niether does anyone else. To know, you'd have to do antibody testing on a scientific sample of the population you are interested in--with enough people in the sample to be statistically significant.
You may already be familiar with this:
Quote:
COVID-19 Antibody Seroprevalence in Santa Clara County, California
Eran Bendavid, Bianca Mulaney, Neeraj Sood, Soleil Shah, Emilia Ling, Rebecca Bromley-Dulfano, Cara Lai, Zoe Weissberg, Rodrigo Saavedra-Walker, James Tedrow, Dona Tversky, Andrew Bogan, Thomas Kupiec, Daniel Eichner, Ribhav Gupta, John Ioannidis, Jay Bhattacharya
2020.04.14
Abstract
Background Addressing COVID-19 is a pressing health and social concern. To date, many epidemic projections and policies addressing COVID-19 have been designed without seroprevalence data to inform epidemic parameters. We measured the seroprevalence of antibodies to SARS-CoV-2 in a community sample drawn from Santa Clara County. Methods On April 3-4, 2020, we tested county residents for antibodies to SARS-CoV-2 using a lateral flow immunoassay. Participants were recruited using Facebook ads targeting a sample of individuals living within the county by demographic and geographic characteristics. We estimate weights to adjust our sample to match the zip code, sex, and race/ethnicity distribution within the county. We report both the weighted and unweighted prevalence of antibodies to SARS-CoV-2. We also adjust for test performance characteristics by combining data from 16 independent samples obtained from manufacturer's data, regulatory submissions, and independent evaluations: 13 samples for specificity (3,324 specimens) and 3 samples for sensitivity (157 specimens). Results The raw prevalence of antibodies to SARS-CoV-2 in our sample was 1.5% (exact binomial 95CI 1.1-2.0%). Test performance specificity in our data was 99.5% (95CI 99.2-99.7%) and sensitivity was 82.8% (95CI 76.0-88.4%). The unweighted prevalence adjusted for test performance characteristics was 1.2% (95CI 0.7-1.8%). After weighting for population demographics of Santa Clara County, the prevalence was 2.8% (95CI 1.3-4.7%), using bootstrap to estimate confidence bounds. These prevalence point estimates imply that 54,000 (95CI 25,000 to 91,000 using weighted prevalence; 23,000 with 95CI 14,000-35,000 using unweighted prevalence) people were infected in Santa Clara County by early April, many more than the approximately 1,000 confirmed cases at the time of the survey.
Conclusions
The estimated population prevalence of SARS-CoV-2 antibodies in Santa Clara County implies that the infection may be much more widespread than indicated by the number of confirmed cases. More studies are needed to improve precision of prevalence estimates. Locally-derived population prevalence estimates should be used to calibrate epidemic and mortality projections.
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https://www.medrxiv.org/content/10.1....14.20062463v2
But this was done in early April. Certainly it's more now.
In San Francisco, tests are now available to pretty much anybody who wants one though it seems likely that people would self-select for suspicion they are infected (symptoms, exposure to an infected person or something). The rate of positivity seems to have stabilized around 3% but that is for current infection using the PCR test and would miss people who were infected many weeks ago and recovered.
https://uniim1.shutterfly.com/ng/ser...670308/enhance
https://data.sfgov.org/stories/s/d96w-cdge
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