Overview of methods for detecting SARS-CoV-2 virus

As a virus enters human cells and replicates, there exists multiple points at which modern medical technologies could detect and assess the abundance of the virus. The first point of contact is the virus itself, where modern reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) could detect the presence/absence of the virus with high sensitivity and reasonable speed. However, assay time and overall cost of each test makes a big difference in the extent in which testing is deployed at the city, state, and national level to contain SARS-CoV-2. PCR tests remain at a relatively high price-point, involves the use of expensive and specialised equipment, and require trained personnel for the test. Herein comes the next approach of detecting some well-conserved fragment of the virus in what is known as an antigen rapid test (ART). In its most typical configuration, the ART test resembles somewhat like a pregnancy test, where the same analytical concept is used to detect some protein on the virus surface. Deployed as a lateral flow assay format, modified antibodies on the assay strip will bind to target antigens from the virus, and deliver a readout in 10 to 30 minutes, all at room temperature, and without the need for specialised equipment. Hence, ART affords high speed and could be deployed at scale such as in pre-event testing, but it is less sensitive compared to PCR test. Beyond detecting the virus itself, there is also value in evaluating whether an individual has been exposed to the virus, has mild or no symptoms, and who is recovering. This then brings forth the use of antibody or serological tests, where the assay kit assesses the IgM and IgG levels of the individual in determining whether he is in the active infection phase or whether he is recovering. For example, a person with high IgM level and low IgG level would be in the active infection phase, and thus, requiring treatment and isolation. On the other hand, a person with low IgM level but high IgG level suggests that he has been previously exposed to the virus, and is recovering. Hence, such serological antibody tests also augment our testing regimen in picking out individuals in the active infection phase, and who require more medical attention. Finally, newly developed breathlyzer tests also provide early indications of a person in the active infection phase, and could serve as a more precise and sensitive screening tool compared to temperature screening. However, the test remains in the evaluation stage, and must be augmented with the gold standard PCR test.