So interesting! How often do you, #asmclinmicro & #AMPath, get asked about Ct values? This manuscript is full of information and the Ct values data is fascinating. https://twitter.com/nejm/status/1253775720972644352

Ct value... an estimate of viral load (VL). The lower the Ct, the higher the VL. With #COVID-19, we have seen Ct in the teens.
2/n Depending on the test, Ct in the teen may represent VL as high as 100,000,000 copies/mL !!

Assumption, high VL (low Ct)...really sick! But surprisingly, not always the case. We’ve seen it and check out Figure ! No symptoms!

Then there is viral culture. Often thought of as the gold standard. But so insensitive. Needs tons of (low Ct) to see CPE in culture. See Figures!

Viral culture =“live” ... ok, so positive VC, should mean symptomatic always while PCR maybe detecting “dead” , so can be ignored? But again those 2 Figures !!

We traditionally don’t measure VL for any respiratory viruses. We traditionally don’t do test of cure or monitor VL for respiratory viruses. Unlike, let’s say CMV in plasma. But even with CMV, it took a long time to standardize VL!

Unlike plasma, a possible limitation of measuring VL or looking @ Ct value in NPS, is that the sample collection has a significant impact on the test result.

We don’t normalize or routinely check for sample quality before PCR. Maybe we should. And then VL in NPS would be more useful? For monitoring treatment or isolation purposes?

Would be curious to know what my colleagues think about Ct values and role in #COVID19 ... @AMPath @ASMicrobiology @GrysClinMicro @SBtotheDub @KarissaPhD @omaigarner @DienBard @UNC_Clin_Micro @E_McElvania