There are two main types of test methods for SARS-CoV-2, the virus that causes COVID-19 disease: molecular tests, which detect the presence of the virus itself; and antibody tests, which look for the past presence of the virus and a possible immune response to the infection.
To test for the virus itself, the most commonly used method involves a nasal or throat swab. The official name is the reverse transcription polymerase chain reaction (RT-PCR). This is a standard molecular testing technique that detects the genetic material of the virus in a respiratory sample obtained by swab.
It can take anywhere from 30 minutes to four hours to get results.
During this time, to test for antibodies, a serological test is used. This tests blood samples obtained from a finger prick. If the diagnosis is positive for antibodies, it shows that a person has been infected with the virus and has developed an immune response.
Antibodies are detectable in the blood, usually around two weeks after infection with COVID-19.
Using standard test methods, both types of tests (molecular amplification and serology) require technical expertise and sophisticated equipment.
What is the rapid test?
Qualified technicians are not widely available to perform PCR tests, which means that there is often an insufficient number of people handling large numbers of patient samples.
Today, many companies are working to simplify and speed up the diagnostic process for detecting COVID-19 and other infections. Some are developing automated PCR machines that reduce the burden on technicians for whom the meticulous sample handling process takes time, while others make easy-to-use paper tests to facilitate testing outside of laboratory settings. These are called rapid diagnostic tests (RDTs).
Earlier this month, scientists in Australia said they had developed a low-cost portable nasal swab molecular test that can diagnose COVID-19 in just 20 minutes.
“When people say ‘rapid diagnostic test’ they are usually referring to those that can be done at or near the bedside, such as routine pregnancy tests, and which can be simple enough to be performed by a health worker. health and [the] visually determined results, even by the patient in some cases, ”Dr Mark Perkins, WHO laboratory team leader, told Al Jazeera.
Antigen detection tests
Enter the antigen test for COVID-19.
Antigens are molecules that stimulate an immune response. Antibodies are proteins produced in response to exposure to antigens.
These new rapid tests use a hand-held device to detect the presence of virus proteins in respiratory samples.
This test technique is cheaper and faster than most PCR tests, giving a result in 30 minutes.
How it works? A sample of body fluid is taken with a swab and applied with liquid to a strip of special paper. The liquid travels along the paper, carrying the antigens with it. If a person is infected, the antibodies bound on the paper capture the antigens, and the indicator dyes tell the user where they were captured.
In May, the United States Food and Drug Administration authorized the emergency use of its first antigen test for COVID-19.
Several states in India have stepped up mass testing with the introduction of rapid antigen test kits.
Perkins said these could potentially “be a game-changer,” making it easier and easier to detect the virus early and easily, especially in developing countries.
“If you live in a small town in a developing country, the chances that there is a PCR machine in your town are low, which is why there is pressure to develop other methods that are simpler. and require less complicated machines, ”he said.
But are they reliable?
WHO researchers continue to assess the accuracy of these antigen detection tests.
Perkins said his team had seen good data on at least four of the dozens of antigen tests in development.
“These antigen detection tests are recently developed and have not been tested on a large scale, but so far they all tend to have relatively high specificity – that is, 98 to 99 percent of people who test positive actually have the infection and only one or two. percent of them are false positive, ”Perkins said.
“The real challenge is to ensure that they are sensitive enough to detect virtually all infectious patients,” he added.
However, there are limits to innovation and the WHO has called for further validation before such tools can be recommended.
The United Nations health agency said: “Inadequate testing can miss patients with active infection or incorrectly classify patients as having the disease when they do not, further hampering the disease control efforts. ”
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