Validation testing to determine the sensitivity of lateral flow testing for asymptomatic SARS-CoV-2 detection in low prevalence settings: Testing frequency and public health messaging is key

Abstract

Lateral flow devices (LFDs) are quickly being implemented for use in large-scale population surveillance programs for SARS-CoV-2 infection in the United Kingdom. These programs have been piloted in city-wide screening in the city of Liverpool and are now being rolled out to support care home visits and the return home of University students for the Christmas break. Here, we present data on the performance of LFDs to test almost 8,000 students at the University of Birmingham between December 2 and December 9, 2020. The performance is validated against almost 800 samples using PCR performed in the University Pillar 2 testing lab and theoretically validated on thousands of Pillar 2 PCR testing results performed on low-prevalence care home testing samples. Our data show that LFDs do not detect infections presenting with PCR Ct values over 29 to 30 as determined using the Thermo Fisher TaqPath asssay. This may be of particular importance in detecting individuals that are either at the early, or late stages of infection, and reinforces the need for frequent, recurrent testing.

Fig 1. Analytical sensitivity and specificity of the Birmingham Turnkey lab RT-PCR pipeline.

This was assessed against the commercial Qnostics SARS-CoV-2 analytical Q-panel– 01. Ct values are a median of 5 independent technical replicates, and figures in parentheses indicate the percentage of replicates returning a PCR positive for that given gene target (Ct <35). Ct, cycle threshold; RT-PCR, reverse transcription PCR; SARS-CoV-2, Severe Acute Respiratory Syndrome Coronavirus 2.

Fig 2. Graph plotting raw Ct values (y-axis) for all 641 positive samples in the Birmingham Turnkey lab (y-axis).

Ct values for each of the targets (Orf1, N, S) are plotted, with a sample only called positive if at least 2 of the 3 targets have a Ct <35. The red line indicates the N gene Ct value equating to 100 viral copies/ml, the previously determined LoD for the Innova LFD. Ct, cycle threshold; LFD, Lateral Flow Device; LoD, Limit of Detection.