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Do we have any idea of what the false-positive rate of these types of tests generally are? It sounds pretty thorough but some actual data on that would be nice.
by anaphor 7y ago
Do we have any idea of what the false-positive rate of these types of tests generally are? It sounds pretty thorough but some actual data on that would be nice.
Also, given that the prevalence of the virus is still very low, I am assuming (and the article seems to support this) that the test would only be used on people that have some pre-existing risk factor, like exposure to a known infected person, or travel to/from one of the high risk locations. Otherwise (let's assume a FP rate of 1%) you would still be getting a large number of false positives. Even with the assumption that there are a large number of very mild undiagnosed cases.
The reason I bring this up is because I have seen many people calling for mass testing of everyone in the United States, regardless of symptoms or risk factors. I think doing that would be a very big mistake because then you end up with a few possible scenarios:
1. You tell everyone who tested positive without any symptoms/high risk factors that they probably don't have it actually.
2. You end up treating massive amounts of people with potentially risky treatments, or quarantine people for no reason.
3. You have to do lengthy/expensive follow up tests of millions of people and waste valuable time and resources.
I guess 1 isn't a big deal, but then how do you prioritize who to treat given the symptoms alone don't provide a very useful criteria for judging who has it?
Obviously the doctors and scientists working on this know all of this already, but the general public and politicians seem to be demanding mass testing of the entire population, which worries me.
- ISL 7y agoFalse negatives may actually pose a greater public-health problem. A suspected case, assayed as a false negative can be released back into the community without quarantine.
- anaphor 7y agoThat's very true. From what I can tell they are focusing on making the false negatives very unlikely for that reason. Do we know how easily it spreads without any symptoms? If someone is exhibiting flu-like symptoms then I'd expect/hope they self isolate and take precautions regardless of whether they test positive or not.
- lacker 7y agoRight now we are releasing everyone who has non-extreme flu symptoms without testing whether it’s flu or covid-19, so even a small false negative rate would be a great improvement.
- code4tee 7y agoIt’s generally hard to have a “false positive” in a PCR based test unless the sample was contaminated with the material trying to be detected. False negatives would be much more common.
- arkades 7y agoMy understanding - from the context of criminal forensics - is that false positives from RTPCR are quite problematic, actually, due to the tendency to pick up non-target DNA that comes close enough to catch the primer. It's an issue in DNA-rich environments (e.g., nasal swabs swarming with local flora). I'm open to learning to the contrary if anyone has a decent citation on the topic.
- tlb 7y agoHuman DNA is extremely similar to any other human, but coronavirus is not very similar to other contaminants. So you need fewer samples of DNA to determine a match. Also, even a few percent chance of error in forensic DNA matching is a huge problem. If a virus test is wrong a few percent of the time it's still useful.
- nostrademons 7y agoWouldn't it be relatively similar to other coronaviruses? With coronavirus causing 15-30% of common colds and it being cold season, that's a lot of potential contaminants. [Actually, the article contains the answer to my objection: they tested for this. The test was developed by explicitly looking for primers that give positive results for known-positive COVID-19 patients but give negative results for other test subjects with common colds or other respiratory illnesses. So assuming they had enough training data, this should already be factored in, and the test should remain accurate. Posting this anyway in case other people are thinking along the same lines...]
- pfarnsworth 7y agoI thought the PCR tests in Asia had a specificity of around 70% which is why they needed two positive tests in a row (or two negative tests in a row to confirm the patient had recovered).
- eyegor 7y agoWhat is "specificity" and do you have a source to back up your claim? (ie, if an individual is infected does it detect it 70% of the time? Or just a true negative 70% of the time? What about the chance of a false negative? A false positive? Etc)
- ivalm 7y agoNot op but specificity is TN/(TN+FP) https://en.m.wikipedia.org/wiki/Sensitivity_and_specificity#Specificity https://en.m.wikipedia.org/wiki/Sensitivity_and_specificity#...