Thread by @yaneerbaryam

Combining PCR and CT testing for COVID: CT-scans can identify who to isolate to stop transmission much better then PCR.

— A thread

Links for the impatient:
necsi.edu/combining-pcr-…
endcoronavirus.org/papers/combini…

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WHAT: The usual COVID PCR test has 30% false negatives: one in three is told they don’t have it when they do. They don’t isolate so many more are infected. CT-scans can see viral pneumonia (including COVID) and isolate people. Then, multiple RT-PCR can be used to confirm COVID.

RESULT: CT-scan compared to PCR by itself reduces cases after 60 days by as much as 50X, reduction of R is 0.20. We can achieve rapid extinction of COVID with social distancing, CT-scans and contact tracing.

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SPEED: PCR test results typically take several days (fast PCR tests have even worse false negative rates). CT-scans take seconds, results can be available within minutes.

Typical pattern looks like ground glass in the lung

(Images paper Ref 1, and healthy lungs)

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AVAILABILITY: PCR tests are now 400,000 per day in the US.

There are about 15,000 CT devices in the US (more than Walmart stores). Efficient intake can enable hundreds of tests per device per day. Potential capacity is millions per day.

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SIMULATION: PCR no CT.

Start with 10 infected individuals run for 60 days. Horizontal bar is individual history: infection, symptoms, test, isolation: pink→presymptomatic, orange→mild, red→severe, yellow→asymptomatic, green→isolated, blackbox→PCR test. Infections about 90

SIMULATION#2: with CT. Dashed blue box → CT-scan. Infections about 38.

Note: Last infection is on day 21.
With PCR alone (previous tweet) outbreak doesn’t stop in 60 days.

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ROBUSTNESS: We did lots of sensitivity tests (see paper): Sensitivity analysis confirms results are robust (Figures 1 and 2 give the main message)

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SUMMARY: Isolate and trace based on CT showing viral pneumonia. Confirm COVID using PCR. Accelerate Coronavirus extinction. Get back to normal. HOW TO WIN!

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FAQs:

1) Aren't CT-scans expensive? For screening a low dose CT-scan without contrast is appropriate. The cost for one can be comparable to RT-PCR

2) What about radiation? The potential for harm from one low dose CT-scan is negligible with minimal risk of adverse consequences