Thread by @letsthinkdeeply

@C1aranMurray @LaurenceBettle The issues on tests; sloppy language often misconstrues their use and value. Data, all data, is good. Misuse and misunderstanding can be very bad.
First, this curve:

@C1aranMurray @LaurenceBettle The disease has two distinct phases with serious disease, this is well known, now. What is less understood is whether there are meaningful long term issues, we do not have objective long term data yet.

@C1aranMurray @LaurenceBettle Then this curve:

@C1aranMurray @LaurenceBettle Without getting into specifics I wish we could be more accurate in the debate. PCR tests detect virus RNA as they cycle multiple times to amplify the amount of viral genetic material so that we can detect it.

@C1aranMurray @LaurenceBettle The PCR issues:

1) over cycling gets sensitive enough that it can find dead virus material and trace contaminants.
2) there are procedural techniques that can avoid errors but they are not uniform.

@C1aranMurray @LaurenceBettle The words “false positive” are used but this is offensive to many. The correct positioning is that an over cycled test does not necessarily indicate active infection and does indicate past infection. There are always small errors in sensitivity and selectivity, too.

@C1aranMurray @LaurenceBettle Small errors are important in that they overstate infection rates where the epidemic has declined. But the the discussion gap is sloppy distinction between active cases and cases no longer contagious. This is further complicated by symptoms being somewhat ambiguous in transition.

@C1aranMurray @LaurenceBettle The same distinction applies to anti-body tests but there is an added issue in that both PCR and AB test positive indications start to decline as time passes.

@C1aranMurray @LaurenceBettle So if the case was not diagnosed early, these tests can yield a true indication of current infection but a false indication of past infection. We have to be careful how we are using tests, and many of us are sloppy in the use of the words “false positive” and “false negative”.

@C1aranMurray @LaurenceBettle Some practitioners and almost all politicians and the press are confused by this discussion. We collectively need to be more precise.