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False negatives are more of an issue in tests for the virus itself, not in antibody tests, correct ?
Not quite. There can be a window of time in which a person is recovering from infection and has started to produce antibodies, but hasn't yet produced a high enough titer of antibody to be detectable on the test. (The RNA viral tests have the same problem in reverse: very early in the infection process, a person may not be shedding enough virus to test positive, even though they are infected.)
The bigger problem with the antibody tests is false positives, though. The specificity of a test is fixed, but the positive predictive value of a test (which tells you how likely it is that a positive result is a real positive rather than a false positive) depends on the percentage of the population who has what you are testing for. If that percentage is too low, false positives can outnumber true positives, which makes the test pretty useless (especially for individual diagnosis). For most of the antibody tests, you want a percentage of infections in the double digits before you can be fairly certain a positive result is actually a true positive. The data coming out of NYC ought to be reliable (especially if the researchers used the newer tests, which have a much better specificity than the earlier ones).
Given that at least 60-70% of people need to be infected in order to achieve herd immunity, though, I wouldn't call a result indicating that only 14% of the population in the single hardest-hit city in the US indicates the virus has spread widely. Rather the opposite! Far more of us have NOT yet become infected by the virus than have.
Edited to add: If you want a more detailed explanation of exactly how the specificity of a test affects positive predictive value, see my post here. Warning, it's long. The explanation starts in paragraph 3.
My girlfriend likely had Covid. No test that I am aware of but many symptoms and her doctor did a CT scan of her lungs which showed that they were inflamed but no pneumonia. It has now been 30 days since she started having symptoms and she seems to be fully recovered.
At what point is it safe to say that she is not contagious? My googling suggests that it should be fine now, but there are some articles talking about six weeks after symptoms go away. I have had no physical contact with her since this started and I don't want to put myself at risk.
72 hours without symptoms is the directive on covid19 for health workers, I believe.
Somewhere between 0.5% and 1% death rate as the NY antibody testing suggests is in line with about 2 million dead if this virus is allowed to infect about 65-70% of the population.
That's assuming all 320 million people in the US get infected, as you get to 60-70% infected, the herd immunity will start to kick in and less and less people should get it.
We don't know as of yet if there is any immunity, or for how long it will last. Could be one and done like chicken pox, none at all, a couple of weeks, a month, who knows?
Somewhere between 0.5% and 1% death rate as the NY antibody testing suggests is in line with about 2 million dead if this virus is allowed to infect about 65-70% of the population.
The rest of the country is far different from NY, in so many ways, that you cannot make a linear extrapolation like that.
The Spanish flu had a death rate of 0.5% so this looks to be significantly more deadly if we assume about 25 000 deaths in the state of New York from those 13.9% infected. That'a assuming that about 4500 more people die over the next 15 days for a total statewide death toll of about 25 000 and they got infected during or prior to the statewide antibody testing.
I think we can also assume that the people in NY are a bit more healthy than the rest of the country, so the death rate might be higher in the rest of the country than NY. On the other hand, NY is slightly older so maybe it evens out.
How can you assume that "people in NY are a bit more healthy than the rest of the country"?
The antibody tests have a 15% false positive, that's for the Abbott test I believe.
I think the tests for the virus itself has more problems with false negatives overall, but I do not think that is conclusive.
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How can you assume that "people in NY are a bit more healthy than the rest of the country"?
People in NY probably have better access to health care than most. Like you, I'm skeptical that they could be more healthy though. They could well have a higher preponderance of people with existing medical conditions, since they are more likely to be rescued from death.
The antibody tests have a 15% false positive, that's for the Abbott test I believe.
I think the tests for the virus itself has more problems with false negatives overall, but I do not think that is conclusive.
Tests don't have a fixed false positive or false negative rate. Those depend on the sensitivity and specificity of the test and the prevalence of what you're testing for in the population you are testing. What is fixed is a test's sensitivity and specificity. Running exactly the same test in two populations with a very different incidence of whatever it is you are testing for can give very different false positive and false negative rates. https://en.wikipedia.org/wiki/Positi...dictive_values
The Abbot test currently has a claimed sensitivity of 100% and specificity of 99.5% (https://www.evaluate.com/vantage/art...ecific-problem). I expect both numbers to go down slightly as most data comes in, as these tests haven't been as thoroughly researched as most new tests are before being brought to market. (In particular, no test is ever 100% sensitive or specific, though greater than 99.5 percent is what most good tests aim for - the higher, the better.)
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