How Covid-19 Diagnostic Test Is Done In Nigeria

Covid-19 (coronavirus) is a pandemic in many countries including Nigeria. It was discovered in 2019 in the city of Wuhan, China. There is no cure or prevention for it yet. The only solution is to test and isolate positive persons while managing their symptoms.

Covid-19 test

Since many people are either asymptomatic or have mild symptoms, it may be difficult to know those who are infected. Such ones can go about spreading the virus to more vulnerable groups. To avoid this, it is good to test as many as possible.
Read Also: Steps to stop to spread of covid-19 around the world

In the beginning due to the unavailability of test kits, the test was available for free to those who come in from high risk countries or have had contact with a confirmed case. However, community transmission on the rise test has made them to expande it to include those who are having covid-19 symptoms in high risk areas.

The first test was designed in January, 2020 by the center for disease control (CDC). That was after China sent in the covid-19 genetic sequence. After some weeks, the CDC sent it out to other laboratories around the world to help them design their own test kits.

There are two types of tests currently in use now. More are under development or about to be deployed. The major one is the polymerase chain reaction (PCR). The other are serological test and medical imaging.

PCR Test

This is the test used in Nigeria. This test is used to detect viral genetic material. The site of interest is the back of the nasal passage. Another one uses saliva. When someone is infected with the virus, it enters the person's bloodstream through the lungs. It can infect cells and make several copies which infect more cells. When there are no more available cells to infect, the excess comes to the back of the nasal passage to be shed of. At this point, the person becomes infectious. However, the test will only be able to pick up the virus some days after the person becomes infectious.

The test will be useless if the body has cleared the virus off the system. At some point, the virus migrates from behind the nasal passage into the lungs where the test will be negative because the swab cannot get there. At that level, the body is winning the war against it.

The process involves inserting a 6 inch long swab into the back of the nasal passage through the nostril. The swab is rotated for some seconds to obtain enough samples. The swab is returned into a container. If it will be transferred to a far distance, it is recommended to be stored in a viral transport media. The sample is sent to the laboratory for analysis and result.

At the laboratory, it passes through four stages. The first stage is sample collection or reception. It involves decontaminating the sample box which may contain several swab.. The next stage is sample inactivation. In this stage, the samples are carefully placed in a glove box for some time. This is done to inactivate the virus to prevent infecting the laboratory staff. The third stage is where the test is done.

Extraction, PCR amplification is the third stage and it involves either Real time (RT-PCR) which is used to amplify the reversed transcription of the DNA code; Quantitative (QPCR) measures the amplification. RT-PCR is for amplification, while qPCR is for quantification.. The genetic material from the sample is copied and then compared to the genetic sequence of the virus. The final stage is the result which takes about 5 to 45 minute for the nasal sample or 24 to 48 hours for the saliva sample.

Serological Test

This is not encouraged by the world health organization (WHO). It is because it does not detect early infection. It only detects that the person has been infected before and is now free of the virus. This test is important for countries who want to know all those who had the virus but where asymptomatic. The test utilizes enzyme linked immunological assay (ELISA) which is the same for HIV. It detects antibodies produced in the body against the virus. Immunoglobulin M (IgM) indicates that the person was recently exposed to the virus but immunoglobulin G (IgG) is for late stage. The test utilizes three sites of the virus. They are human RNA polymerase protein (Orf1), nucleocapsid protein (N-gene) and envelope protein (S-gene) which is limited. The reason why this is important is that if one of the virus sites mutate, the others will still be detected.

Medical Imaging

Since the covid-19 is a disease of the respiratory tract, medical imaging gives some form of information about the infection. Although, it requires a confirmation test from PCR.
Read Also: List of diagnostic test

Others

Presently there are several tests under development and some few ones soon to be deployed. Very few information is available about their working principle.

Rapid Molecular Test

The tuberculosis test kit is in many african countries. This is because tuberculosis is rampant in many african countries. The tuberculosis test kit uses a cartridge to run the test. Cepheid developed a test kit in the form of a cartridge. This cartridge can fit into the slot of a tuberculosis test kit and give out results. This may increase the test capacity of many african countries. However, the cost of the cartridge is yet unknown which may hinder the successful deployment.

Isothermal nucleic amplification, Rapid in-clinic antigen testing and Lateral flow rate using biological markers are on the way.

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