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 .