Thread by @deeksj

Well here is some real data from 27 health care workers who picked up symptomatic Covid-19 infections whilst being tested twice weekly using RT-PCR. The paper develops models to look at impact of testing frequency, but also hypotheses on LFT performance
bmcmedicine.biomedcentral.com/articles/10.11…

There is excellent presentation of the original data in the paper, as well as results from the models. Kudos to the authors.

Plots of Ct values from PCR are provided, which show that RT-PCR with Ct<37 had a peak sensitivity for detecting infection of 77% 4 days after infection.

No LFTs were used in the study, but the paper considered test results with Ct<28 and Ct<25 as illustrations of how LFTs might perform. At Ct<28 the red spots are +ve LFT results, the black are -ve LFT results, peak sensitivity is 64% at 4.3 days post infection.

At Ct<25 (the lower limit of detection reported by PHE for Innova) the picture is here. Peak sensitiivty is down to 42% 3.8 days after infection.

There have been many ad hoc reports of HCWs becoming symptomatic before their LFTs become positive - these data give some insight that low sensitivity tests are not fit for this purpose - reducing sensitivity from 77% to 42%. Poor tests miss and delay detection of infection.