4.1. Current diagnostic methods
It is to be appreciated how technology has advanced to a level where we can now detect and identify the causative organism of an unknown infection rapidly. In times of medical emergencies, as in a pandemic like COVID-19, multiple clinical priorities are starting from the need to understand the pathology of the disease to provide effective treatment to the patients . Since the beginning of the pandemic, a lot of efforts have been put into developing accurate and rapid diagnostic techniques to detect SARS-CoV-2 infection in patients, to reduce the risk of spread of the infection as well to promptly provide treatments for the infected patients . The current diagnostic methods can be understood as under two categories: 1) direct detection where the procedure mainly involves detection of viral proteins or nucleic acids and 2) molecular or immunological tests that aim to detect virus-specific antibodies in the patients .
Among all the various methods available so far, the two major tests currently in use to detect the SARS-CoV-2 infection are molecular methods and serological methods, which can be used irrespective of the viral variant causing the infection . Molecular methods, more specifically nucleic acid-based methods generally make use of the genetic material of the virus (single-stranded RNA in the case of Sars-CoV-2), and they are based on the principle of high specificity base pairing between homologous strands . Real Time-Polymerase Chain Reaction (RT-PCR) is one such method that is widely used with high sensitivity and specificity with the added benefit of quantification of viral RNA . NGS is used to obtain the sequence of the viral genome and this way it helps to detect the mutations that have given rise to the variants . Immunological assays like antibody-based assays or antigen-based assays are also in use. However, diagnosing COVID-19 infection in the early stages using an antibody-based method becomes difficult. As the body takes time to recognize novel foreign antigens and produce appropriate antibodies, thus giving rise to false-negative test results . Sometimes patients have advised a computed tomography scan (CT scan) of the lungs to check for cases of viral pneumonia or other similar abnormalities. However, these scan results cannot on their own be used as a positive confirmation of the infection and need to be accompanied by other nucleic acid or molecular test results because CT scan results are not as sensitive as RT-PCR . The different methods of detection and identification of COVID-19 are currently in use as shown in Figure 2 .