MARCH 26 — There are many countries and companies pushing their test kits, some with exaggerated claims and others simply fraudulent. To ensure that these are genuine and evidence based one needs to be familiar with the response of the body to the presence of SARS-CoV-2 in our upper airway and later in our blood stream.
Swabs of the naso-pharynx (into the nose and back of throat) or the oro-pharynx (into the mouth and back of the throat) is best subjected to rt-PCR (reverse transcriptase-Polymerase Chain Reaction) test, which detects the genomic sequence of SARS-CoV-2.
This the best test for the acute phase of the illness when the patient does not even display any symptoms or signs of Covid-19 disease. The turnaround time is 24 hours at best. And it remains the gold standard.
However, the WHO test protocol for rt-PCR is complex, expensive, and is only suited to large, centralised diagnostic laboratories.
There is therefore an urgent need to decentralise testing to the point-of-care (POC) testing with rapid diagnostic kits as per our experience with dengue diagnosis.
These kits needs to be rapidly validated, implemented and distributed to enhance our frontline response to the SARS-CoV-2 outbreak, to diagnose early and promptly isolated to prevent its spread.
The period between exposure and showing signs or symptoms of Covid-19 is the Incubation Period (IP). The average IP is 7 days with a range of 2-14 days. This coincides with the appearance of the antigen in the blood. The antigen immunoassay test will only be useful after the onset of the symptoms.
The test is less accurate compared to rt-PCR but they are cheaper, easy to use and deliver results within 20-60 minutes. The MOH is presently validating this test.
The myeg Covid-19 rapid test kit and the similar has been bandied as the solution to the need to accelerate diagnosis during a public health emergency.
The IgM and IgG antibodies which the antibody immunoassay detects only appears 7-14 days into the Covid-19 illness. It may therefore miss the early and asymptomatic phase of the illness.
But it is easy to use at the POC, is cheaper and more useful to ascertain the extent of spread into the community and spread by asymptomatic or mild Covid-19 disease.
Both the antigen and antibody immunoassays has only a limited role if tested and interpreted as a single assay. It will undoubtedly complement the Covid-19 rt-PCR.
A game changer in the race to produce a point of care diagnostic test kit is the Cepat kit from Singapore which is awaiting approval from the regulatory authorities.
Acting on the secretions collected from a nasopharyngeal, Cepat, using a special enzyme, rapidly amplifies the SARS-CoV-2 genetic material million of times, so that it can then be easily detected in as early as 5-10 minutes.
When approved, Cepat would be the fastest test kit to diagnose Coved-19.
* Datuk Dr Musa Nordin is a paediatrician
** This is the personal opinion of the writer or publication and does not necessarily represent the views of Malay Mail.