PCR testing & the CDC controversy. Some thoughts.

Per fascinating paper (see below), we are likely (1) infectious no more than 9d; (2) but can carry VL/test PCR + up to 80d.

So PCR positivity (w/o timing info) does NOT tell us much.

How do we get timing info?

In case of a symptomatic infection, we can presumably infer when the person became infected from details surrounding the onset of symptoms.

This context can help us discern whether we are picking up recent or older (non-infectious) VL.

But things get trickier with asymp.

For asymp, can't rely on timing of symptoms of course.

And with purely prophylactic testing--like at colleges--nor can we infer timing from exposure, as testing is w/o regard to exposure.

So, we end up then w/ just PCR+, but no timing info. Which, again, tells us nothing.

Without any information as to the timing of infection, we can't reliably say whether the person is infectious.

Thus, when it comes to allocating finite tests, there would seem to be a compelling argument for de-prioritize testing of asymptomatics.

Here is the paper I am relying on. https://medrxiv.org/content/10.1101/2020.07.25.20162107v2

Here is a great thread from the brilliant author summarizing the paper. https://twitter.com/mugecevik/status/1288440970355376128?s=20