As of April 16, 2020, there were more than two million confirmed infections of SARS-CoV-2, the virus responsible for Coronavirus Disease 2019 (COVID-19), around the world. In the battle against this rapidly expanding pandemic, successful COVID-19 community screening programs are essential for assessing infection prevalence, aiding identification of infected patients, and enacting appropriate treatment and quarantine protocols.
When initially screening for COVID-19 infections, many assay chemistries used Reverse Transcriptase PCR (RT-PCR) methods to detect live virus. This live virus method, however, has serious limitations that the healthcare community cannot ignore. RNA testing has high false negative rates with naso/oropharyngeal swab samples (30%–75% sensitivity during the first two weeks of infection) due to inconsistent swab technique or low viral titers in the sampled body compartments.1 If an individual receives false negative results, they may relax quarantine precautions and unintentionally expose others to the virus. Additionally, if materials such as nasopharyngeal swabs and extraction kits are in short supply, they limit test capacity and cap the number of assays that a testing site can perform. Moreover, live virus RNA-based assays only detect acute infection and cannot be used to capture meaningful data on individuals who have cleared the virus or provide immunity information.
With these limitations, it is clear that there is an urgent, unmet need for a sensitive and specific liquid biopsy test to complement live virus RNA-based assays and improve disease identification and tracking. Unlike live virus RNA-based assays, liquid biopsy DNA-based assays use qPCR to detect the individual’s antibody response to the pathogen, and so may provide information critical for serum-based immunotherapies. Those assay methods employ ELISA and lateral-flow, which may have a relatively low sensitivity leading to a high degree of false negatives, especially when a large proportion of infected individuals are in the acute disease stage and have low antibody levels.
Antibody Detection by Agglutination-PCR (ADAP) differs from traditional immunoassays in that it is a pure solution phase assay, it is well suited to detecting conformationally challenging antibodies, and it requires little in terms of input sample volume. The assay uses a pair of antigen-DNA conjugates to probe the sample target antibodies. If present, agglutination between the antibody and antigen, and ligation, leads to formation of a specific DNA amplicon detected by qPCR.