Thread by @DavidJuncker

🧵Are rapid tests working with #omicron and how to use them?

The analytical performance of RAT vs PCR seems unchanged, but the capacity to detect infectious cases when used as instructed appears to be lower.

Two contradictory preprints, and anecdotes feed this analysis.
1/n

Abbott BinaxNow vs PCR,
Both nose swabbing, RAT first, then PCR

Excellent concordance up to CT<30, roughly the threshold where samples remain infectious when incubated in cell culture.
medrxiv.org/content/10.110…

➡️RAT Analytical performance is preserved with omicron
2/n

BinaxNow and Quidel Quickvue vs PCR.
RATs based on nose swab, PCR using saliva.

Many false negative results in the first two days w. very high viral load CT<30.

➡️Virus lags in the nose vs saliva
➡️Nose swabbing vs saliva leads to initial false negative RAT (and PCR)
3/n

⚠️High saliva CT values suggest patients are infectious while RATs are negative. ⚠️

Virus appearing first in saliva and throat supported by numerous accounts of people getting a positive tests only after swabbing throat:

https://twitter.com/JennyRohn/status/1475410068019585027?s=20

4/n

Sampling is back: remember the challenges about sampling early in the pandemic when estimates of PCR sensitivity where 70% because of sampling

Omicron, which reproduces much faster is muddling the waters when it comes to sampling:

https://twitter.com/DrAnneCarpenter/status/1478336456385040386?s=20

5/n

Rapid tests were not approved for tongue and throat swabbing

@FDA and @michaelmina_lab don't recommend it

https://twitter.com/michaelmina_lab/status/1479895484701552641?s=20

Should we consider it?

YES, because we are in a pandemic, some tests are approved for dual sampling, and risk-benefit analysis supports it
6/n

@FDA and @GovCanHealth approved RATs for the original strain, but this is a different disease that spreads uncontrollably and follows a different dynamic.

https://twitter.com/michaelmina_lab/status/1478799576693891072?s=20

7/n

The biggest failure would be to do nothing

Remember @DrMikeRyan words of wisdom and warning from March 13th 2020:

https://twitter.com/doritoribio/status/1239326086045077506

8/n

If throat tongue sampling for RATs were to lead to false positives or negatives, it would already have been relayed and amplified on twitter.

Knowing RAT kits, and the comparatively large buffer volumes, we expect them to work.

9/n

Nose swabbing only means high risk of false negative test and of spreading omicron = high risk. Any benefit?

The added benefit of detecting cases thanks to throat and tongue swabbing (and nose swabbing) is large, while the risk of compromising the tests is low.

10/n

CONCLUSION: Rapid tests work with #omicron, but swab tonsils and tongue before swabbing the two nostrils on two consecutive days (if negative on first day) as @Bob_Wachter explains it:

https://twitter.com/Bob_Wachter/status/1479913175860465665?s=20

If symptoms persist, stay home.
11/n

I meant to say low CT values in saliva.