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I am an engineer and currently doing some modeling of COVID-19 testing from a math perspective. I was reading through COVID-19 articles related to testing and I had the following doubt:

If a specimen is collected from a person through some swab (say, a nasal swab), can I only use it for one COVID-19 viral test?

I understand that logically, there will be dilution effects if I make multiple test samples from a single swab specimen. But, practically is it possible to "split" the specimen so as to do multiple tests.

Also, can someone point me to authentic sources which talk about splitting specimen collected through a single swab for multiple tests?

Any comments are appreciated :)

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  • What purpose do you envision for your multiple subsamples? – cbeleites unhappy with SX May 2 '20 at 11:33
  • Could you link your sources, please? – Thomas May 3 '20 at 7:48
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When you're doing a nasopharyngeal swab you want primarily cellular material that is infected with virus. You can cut the tip of the swab successfully as in this study for multiple tests

Study design

We collected a NP swab on children aged 2–12 years with acute sinusitis and processed it for bacterial culture, viruses, cytokine expression, and 16S ribosomal RNA gene sequencing analysis. During the course of the study, we expand the scope of evaluation to include RNA sequencing, which we accomplished by cutting the tip of the swab.

Results

Of the 174 children enrolled, 126 (72.4%) had a positive bacterial culture and 121(69.5%) tested positive for a virus. Cytokine measurement, as judged by the adequate levels of a housekeeping enzyme (GAPDH), appeared successful. From the samples used for 16S ribosomal sequencing we recovered, on average, 16,000 sequences per sample, accounting for a total of 2,646 operational taxonomic units across all samples sequenced. Samples used for RNA sequencing had a mean RNA Integrity number of 6.0. Cutting the tip of the swab did not affect the recovery yield for viruses or bacteria, nor did it affect species richness in microbiome analysis.

But if you're asking about COVID-19, saliva may be better than a swab. In any case you're talking about a test (rt-PCR) that can amplify very small numbers of virions present.

A method of processing nasopharyngeal swabs to enable multiple testing https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6851467/

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