This can only be used on groups where everyone is asymptomatic, and there will be low limits on the pool size even then.
The first step of a PCR test is RNA amplification; you use enzymes which take a small amount of RNA in the sample, and produce a large number of copies. The problem is that there are other RNA viruses besides SARS-CoV-2, such as influenza, and depending when in the disease course the samples were taken, the amount of irrelevant RNA might exceed the amount of SARS-CoV-2 RNA by orders of magnitude, which would lead to a false negative.
1) The threshold for detecting the (very similar) SARS virus was 37~4000 copies per mL (depending on the platform—this suggests that choice of platform will be critical for this to work well) https://jcm.asm.org/content/42/5/2094
I certainly agree that there’s a very very good chance that no lives will be saved if we do a great job quantifying the potential benefits of test-pooling and disseminating that information. But I still think it’s an activity with a sufficiently high expected value as to be worth someone’s time to do … compared to other ways that theoretical CS types could be spending their time to “help the war effort” :-)
This appears to be the university press release, if you consider that to be more reliable:
According to Prof. Roy Kishony, head of the research group in the Faculty of Biology at Technion, “This is not a scientific breakthrough, but a demonstration of the effectivity of using the existing method and even the existing equipment to significantly increase the volume of samples tested per day. This is done by pooling multiple samples in a single test tube. Even when we conducted a joint examination of 64 samples in which only one was a positive carrier, the system identified that there was a positive sample. Although there are some logistical challenges in implementing the method, we expect that it will greatly increase the volume of samples tested per day so that we can identify the asymptomatic carriers. This approach should reduce the chance of infection and flatten the infection curve.”
One hopes that the university wouldn’t misquote one of their own professors in their own press release :)
The problem is that there are other RNA viruses besides SARS-CoV-2, such as influenza, and depending when in the disease course the samples were taken, the amount of irrelevant RNA might exceed the amount of SARS-CoV-2 RNA by orders of magnitude
There is going to be tons of RNA in saliva from sources besides SARS-CoV-2 always. Bits of RNA are floating around everywhere. Yes, there is some minimum threshold of SARS-CoV-2 density at which the test will fail to detect it, but this should just scale up by a factor of N when pooling over N people. I don’t see why other RNA those people have will be a problem any more than the other sources of RNA in a single person are a problem for a non-pooled test.
This can only be used on groups where everyone is asymptomatic, and there will be low limits on the pool size even then.
The first step of a PCR test is RNA amplification; you use enzymes which take a small amount of RNA in the sample, and produce a large number of copies. The problem is that there are other RNA viruses besides SARS-CoV-2, such as influenza, and depending when in the disease course the samples were taken, the amount of irrelevant RNA might exceed the amount of SARS-CoV-2 RNA by orders of magnitude, which would lead to a false negative.
Did you read the link at the top? It says it works for 64 people, right? Is that article unreliable or misleading or something?
It’s a newspaper article based on an unpublished paper; that reference class of writing can’t be trusted to report the caveats.
(I could be wrong about the mechanics of PCR; I’m not an expert in it; but the article itself doesn’t provide much information about that.)
Pre-print of the paper with details of the methods, etc: https://www.medrxiv.org/content/10.1101/2020.03.26.20039438v1.full.pdf
Similar methodology, but with pools of 10:
https://www.medrxiv.org/content/10.1101/2020.03.30.20043513v1.full.pdf
Peer-reviewed paper with pools of up to 96 samples for avian influenza:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2878216/
None of this is surprising given that...
1) The threshold for detecting the (very similar) SARS virus was 37~4000 copies per mL (depending on the platform—this suggests that choice of platform will be critical for this to work well) https://jcm.asm.org/content/42/5/2094
2) Patients with COVID-19 generally have 10,000 to 1,000,000 copies per swab. Not sure how many mL per swab, but not many I suspect: https://www.nature.com/articles/s41586-020-2196-x_reference.pdf
3) PCR uses primers to selectively amplify only the target RNA. The presence of other RNA is not really a problem
...
Put it all together and here is the argument: https://www.medrxiv.org/content/10.1101/2020.03.27.20043968v1.full.pdf
I certainly agree that there’s a very very good chance that no lives will be saved if we do a great job quantifying the potential benefits of test-pooling and disseminating that information. But I still think it’s an activity with a sufficiently high expected value as to be worth someone’s time to do … compared to other ways that theoretical CS types could be spending their time to “help the war effort” :-)
This appears to be the university press release, if you consider that to be more reliable:
One hopes that the university wouldn’t misquote one of their own professors in their own press release :)
There is going to be tons of RNA in saliva from sources besides SARS-CoV-2 always. Bits of RNA are floating around everywhere. Yes, there is some minimum threshold of SARS-CoV-2 density at which the test will fail to detect it, but this should just scale up by a factor of N when pooling over N people. I don’t see why other RNA those people have will be a problem any more than the other sources of RNA in a single person are a problem for a non-pooled test.