Number one comment of concern I receive about why we can't deploy rapid daily #COVID19 tests that test for people with likely transmissible virus:

"We can't do this yet because we don't know the exact cutoff viral load for transmissibility"

This misses the point...

1/n

We KNOW that transmission occurs when viral loads are high

We know people are likely transmissible a couple days prior, to ~1 week after symptom onset. And we know during this time, virus is often MUCH HIGHER (10,000x - 1,000,000,000x) than the limit of detection of PCR)..

2/n

So we don't need to wait for human transmission experiments (won't happen) to solve this.

We know enough to know what will help. And a test that detects within 1000x the limit of detection of PCR will be more than sufficient to detect most people who are transmitting.

3/n

We can't allow imperfect knowledge slow us and prevent us from fixing a massive problem that is right now killing hundreds of thousands of people

We know enough- we don't need an exact cutoff and, frankly, there will not be an exact cutoff. Transmission is much more complex

4/4

Final thought - Even IF some ppl can transmit when viral load is <1000x the limit of PCR, getting daily tests to millions of ppl that can detect >1000x the limit will catch MOST people when infectious. Public health tests don't need to be perfect to stop raging outbreaks.

They just need to break enough transmission chains to bring R way below one. And all evidence suggests that a daily test for everyone that tells people exactly when to isolate would do this very quickly. These are transmission blocking tests. Not diagnostic and not perfect.