Soft drinks can be misused to give false false positive SARS-CoV-2 lateral flow device results

Background The COVID-19 pandemic created the need for very large scale, rapid testing to prevent and contain transmission of the SARS-CoV-2 virus. Lateral flow device (LFD) immunoassays meet this need by indicating the presence of SARS-CoV-2 antigen from nose/throat swab washings in 30 minutes without laboratory processing, and can be manufactured quickly at low cost. Since March 2021, UK schools have asked pupils without symptoms to test twice weekly. Pupils have posted on social media about using soft drinks to create positive results. The aim of this study was to systematically test a variety soft drinks to determine whether they can cause false false positive LFD results. Methods This study used 14 soft drinks and 4 artificial sweeteners to determine the outcome of misusing them as analyte for the Innova SARS-CoV-2 antigen rapid qualitative LFD. The pH value, sugar content and ingredients of each sample are described. The LFD results were double read and a subset was repeated using the same devices and fake analytes but differently sourced. Findings One sample (1/14; 7%), spring water, produced a negative result. Ten drinks (10/14; 71%) produced a positive or weakly positive result. Three samples (3/14; 21%) produced void results, mostly the fruit concentrate drinks. There was no apparent correlation between the pH value (pH 5.0 in 13/14, 93%; pH 6.5 in 1/14; 7%) or the sugar content (range 0-10.7 grams per 100mls) of the drinks and their LFD result. The 4 artificial sweeteners all produced negative results. A subset of the results was fully replicated with differently sourced materials. Interpretation Several soft drinks can be misused to give false positive SARS-CoV-2 LFD results. Daily LFD testing should be performed first thing in the morning, prior to the consumption of any food or drinks, and supervised where feasible. Funding This work was self-funded by author LO and the LFD were gifted for use in this study.

More than the eye can see – shedding new light on SARS-CoV-2 Lateral Flow Device-based immunoassays

Containing the global SARS-CoV-2 pandemic has been an unprecedented challenge due to high rates of both horizontal transmissivity and asymptomatic carriage. Lateral Flow Device (LFD) immunoassays were introduced in late 2020 to rapidly detect SARS-CoV-2 infection in asymptomatic or pre-symptomatic individuals in the population. Although LFD technologies have been used for over 60 years, their widespread use as a public health tool during a pandemic is unprecedented. By the end of 2020, data from studies into the efficacy of the LFDs emerged and showed these point-of-care devices to have very high specificity (ability to identify true negatives), but inadequate sensitivity with high false-negative rates. In particular, the low sensitivity (<50%) shown in several studies is a critical public health concern, given that asymptomatic or pre-symptomatic carriers may wrongly be assumed to be non-infectious, and posing a significant risk of further spread in the community. Here we show that the direct visual readout of SARS-CoV-2 LFDs is an inadequate approach to discriminate a potentially infective viral concentration in a bio-sample. Using high sensitivity synchrotron X-ray fluorescence imaging we were able to quantify significant immobilized antigen-antibody-label conjugates within the LFDs visually scored as negative. Correlating quantitative X-ray fluorescence measurements and qRT-PCR determined numbers of viral copies we identified that negatively scored samples could contain up to 100 PFU (equivalent here to ∼10,000 RNA copies/test). This is of significant concern should these tests be used to control community spread. The study demonstrates where the shortcomings arise in many of the current direct-readout SARS-CoV-2 LFDs, namely being a deficiency in the readout as opposed to the potential level of detection of the test which is orders of magnitude higher. Our findings are of importance both to public health monitoring during the COVID-19 pandemic and to the rapid refinement of these tools for immediate and future applications.