Mohamed Ibrahim Bassyouni
2020 / 6 / 28
Countries of the world use several types of tests to detect the Corona virus in order to determine the number of infections and to develop plans and measures to control the spread of the disease. To date, there are more than 150 types of corona virus detection tests. In general, these tests can be divided into two groups:
The first group is diagnostic tests that reveal whether a person is infected with the virus at the present time and is able to transmit infection to others, while the second group is tests that reveal whether a person has been infected with the virus in the past and recovered from it.
First, in order to diagnose a person s infection with the virus, a test known as PCR PCR´-or-"polymerase chain reaction" may be used. Tests called "isothermal DNA amplification" can also be used, which is very similar to "PCR". In both cases swabs of saliva are taken with a lumbar stick from the upper respiratory tract of the person, that is, throat, nose and mouth. It is also possible to take samples from the lungs as well.
The specialists then analyze the sample to determine whether it contains the genotype of the Coronavirus. If the virus is found to have a genetic´-or-"genome" in the sample, this means that the owner of the sample is a carrier of the disease. But we must pay attention to the fact that the lack of a genetic factor in the sample does not necessarily mean that a person does not carry the virus, as the virus may already be in his body but in other parts of which no samples were taken.
A swab is usually taken from the mouth´-or-throat to diagnose the Coronavirus.
This explains some of the cases that doctors thought had recovered from Corona, and then the results of their sample tests were positive after their discharge. It is likely that they were carriers of the virus the entire time, but it did not appear in the samples that doctors took them from before they were discharged from the hospital, which led to doctors believing that they had recovered.
The second set of corona virus detection tests are antibody tests and work with a technique called "ELISA", an enzymatic immune technique that shows whether a person has been infected with the virus in the past.
When the virus infects the body, the immune system builds up antibodies to fight it. And if these antibodies are found in the sample, this means that the person was infected with corona at some point. This test is done by taking a blood sample from the person, which is then analyzed.
Several companies have produced rapid-detection antibody detection tests, and if the antibodies that the body makes against the new coronavirus are present in the blood, called “IgM” and “IgG,” the color of the sample changes. This means that this person had been infected with the virus in the past if it were positive for IgG and had immunity to it. If it is positive for IgM, the infection is recent.
The results are not always guaranteed, sometimes a so-called "cross-reactivity" occurs, that is, the interaction of antibodies with another Coronavirus-like virus. This means that even if the result of this test is positive, the antibodies that make up the body may have been resistant to other respiratory infections from the Coronavirus family, such as a common cold. However, the producers of these tests deny this happening with their products and confirm the validity of the results.
A positive antibody test result means that a person has been infected with the Corona virus in the past, but there are some exceptions.
The importance of the PCR Corona Diagnostic Screening test is due to its ability to identify people infected with the virus, which makes it possible to reach the circle of their mixing and determine appropriate isolation procedures for them, whether by two-week preventive isolation´-or-quarantine in more severe cases.
The "ELISA" antibody tests help epidemiologists know the number of people who have been infected in the past and have not been counted in official statistics, and this test also helps to know whether numbers indicate access to a type of "herd immunity" in society. This helps decision-makers in countries take appropriate measures to ease´-or-tighten restrictions.
In addition, the antibody test helps in vaccine tests that are conducted on volunteers to monitor the reaction of their immune system. It is also possible through this test to follow the immune system of people who have already infected and recovered from corona. Indeed, some university hospitals began using "ELISA" tests on a random sample of participants to find out if they were infected, as well as to study the behavior and evolution of the virus.
Countries differ in their treatment of Corona virus tests for several reasons, such as the capabilities of health systems in each country and the availability of tests and laboratory equipment needed to conduct them. The behavior of countries varies in the seriousness of dealing with the pandemic.