Read this article to get an insight into the methods and protocols of COVID-19 testing.
Rapid testing and vaccinations play a crucial role in breaking the transmission chain of coronavirus. Earlier, only polymerase chain reaction (PCR) and antibody testing were available. Now, there are a number of tests to detect both current and past infections. One such evolution is the development of a self-testing COVID-19 kit.
Ideally, during any infectious disease outbreak, public health officials begin testing for it early. This leads to the quick identification of cases, prompt treatment, and immediate isolation to prevent spread. Testing also helps in the early identification of people who came in contact with the infected people to prevent unconscious spread.
A lack of early testing has resulted in a rapid rise in hospitalizations, overburdening the healthcare system. In countries like South Korea and China, as tests were readily available when the first few cases was reported, they managed to drastically lower the death rate compared to other countries, such as the UK and the US.
Apart from diagnosing an active COVID-19 infection, the other important test is the one that determines the previous COVID-19 infection. When we get infected with a virus, our immune system fights the virus and protects us by producing antibodies. These antibodies can be detected with the help of blood tests. Even though the individual might not be infectious any longer, the information about past infections can be extremely valuable. Information about immunity to the new coronavirus can be obtained from this. Also, plasma from such recovered patients can be used to treat others with an active infection which is called convalescent plasma therapy.
There are two types of tests available for COVID-19 testing, which include diagnostic tests and antibody tests. Antigen and molecular tests are the two types of diagnostic tests that help in detecting a current infection, while antibody tests detect a past disease.
1) Molecular Tests or RT-PCR Testing:
Presently, the majority of COVID-19 reports are coming from RT-PCR (reverse transcription-polymerase chain reaction), and it is the gold-standard test for COVID-19. RT-PCR first converts viral RNA into DNA, then amplifies that DNA. PCR (polymerase chain reaction) amplifies or replicates a small segment of the DNA several thousands of times, making it easy to be detected. As SARS-CoV-2 is an RNA virus that contains RNA, RT-PCR can help detect them. This test requires a few hours. The detection of viral RNA is only possible when the virus is present in the body, and someone is actively infected. Viral RNA is present in the body before antibodies get formed or signs and symptoms develop. As a result, this test helps in diagnosis much early.
The likelihood of this test detecting the virus depends on the collection method and the time passed since infection. Throat swabs are only recommended in the first week, as the virus moves deeper into the respiratory tract, multiplies in the lungs, and abandons the throat. During the second week, sputum collection is preferred. The samples can be obtained by throat swabs, nasopharyngeal swabs, sputum, or saliva. Nasal and throat swabs are 63% sensitive to RT-PCR, the pharyngeal swab is 32%, and the sputum is almost 75% sensitive.
PCR is beneficial when it comes to identifying individuals early in the course of infection. Such individuals can be isolated, and their contacts (people they came in contact with) can be quarantined too. It helps in breaking the transmission chain.
RT-PCR can be labor-intensive, and as it is such an extensive process, errors can happen anywhere from sampling to analysis. 30% of the time, the reports can be false-negative.
2) Rapid Antigen Test:
The part of the virus that makes the body produce antibodies is called an antigen. SARS-CoV-2 antigen test looks for antigen proteins in the virus’s surface spikes. These antigens can be detected before the onset of symptoms, but this test is less sensitive than the PCR test. But, as the PCR test takes up so much time and is expensive, the antigen test is the way to scale up testing to a much greater level.
Here, samples are collected through nasopharyngeal swabs or saliva. The collected sample is then exposed to strips that contain artificial antibodies. The antigen present in the sample will bind to the coronavirus antigens on the strip and give a visual result.
This test is simple to do and takes less than 30 minutes. No expensive equipment or training is required and does not require a visit to the laboratory. This test does not require deeper swab insertion; taking samples from the nares (openings of the nasal cavity) is adequate. In October 2021, the FDA made it a point to make the rapid test kits available over the counters so that identifying the infection is more effortless and facilitates timely isolation, thereby limiting the spread.
Throat and nasal swabs of respiratory viruses usually lack detectable viral antigen. This is more commonly seen in asymptomatic patients, as they have little to no nasal discharge. As the viral antigen is not replicated in antigen testing, the available antigen might be too little to get detected and might show false-negative results.
As the antigen test is only reliable if the viral load is high in the body, various doctors do not recommend getting it. At the same time, others argue that people with high viral load are highly infectious, and by mass screening, such individuals can be identified. Also, in august 2021, a query arose on the test sensitivity after vaccination, if it will experience a fall due to the reduction in viral load. It is still on research in the U.S.
3) Antibody Tests:
This test detects the antibodies produced by our body to the viral antigen. Serology or blood tests can detect such antibodies. Antibody tests might not tell if the person has an active infection, but they can be used to assess the percentage of a population that has already been infected. A positive antibody test implies that antibodies are present either from a previous infection or from vaccination. It is also not clear if mild or asymptomatic patients produce sufficient detectable antibodies. The types of antibodies test that can be used to identify antibodies against SARS-CoV-2 are-
Rapid diagnostic test (RDT).
Enzyme-linked immunosorbent assay (ELISA).
Antibody testing will help identify the number of people in a population who are immune to the virus. Such immunity will stop frequent outbreaks of the new Coronavirus within the population. This is called herd immunity. In case someone gets infected, the virus will not be able to spread to others as long as others are immune.
On 17th November 2020, the U.S. Food and Drug Administration (FDA) issued a EUA (emergency use authorization) for a rapid COVID-19 self-testing kit. This kit is called Lucira COVID-19 All-In-One Test Kit, a single-use test that can detect the SARS-CoV-2 virus responsible for causing COVID-19. People can use this kit to test for COVID-19 by self-collected nasal swab samples. This kit can also be used in hospitals, clinics, and emergency rooms if a healthcare provider collects the sample. These self-test kits can be used by self (14 years or above) or for kids ( two year and above) under supervision of adults.
The nasal swab sample has to be swirled in a vial placed in the test unit. In about 30 minutes, the test unit's light-up display shows whether the person is positive or negative for the SARS-CoV-2 virus.
If you followed the instructions correctly and your test report shows negative results, you do not have an infection. However, it is advisable to get serial testing done as mentioned by the manufacturer to prevent the chance of the spread of the virus. If you get a positive report, immediate medical intervention is needed by a healthcare professional. Also, you should make sure to follow the necessary guidelines to prevent the spread of the virus.
Currently available over-the-counter at-home COVID tests are as follows-
Andrew Books developed the saliva test in which, instead of the nasal swab or throat swab, a saliva sample was taken to diagnose COVID-19. These tests provided more consistent and accurate results. Even individuals with mild infections tested false-negative for nasal swabs showed positive reports with a saliva test. Saliva tests reduce the risk of exposure to the medical professional taking the test because it does not produce sneezing or coughing. Some home tests use saliva to determine the presence of COVID-19 infection.
In April 2022, FDA gave emergency use authorization (EUA) to use of SARS-CoV-2 diagnostic tests that analyze breath samples. One such example is InspectIR COVID-19 Breathalyzer. Exhaled breath samples from people aged 18 and above with or without symptoms or other epidemiological reasons to suspect COVID-19 were found to contain five volatile organic compounds (VOCs) from the ketone and aldehyde families linked to SARS-CoV-2 infection. Only authorised settings can utilise this test in an emergency.
1. People who have symptoms of COVID-19.
2. Individuals who have come in contact with COVID-19 infected people should take their tests in the following ways:
3. Unvaccinated people who have participated in activities with an increased risk of disease contraction.
4. Individuals who have been asked to get tested.
Testing is a significant tool to reduce the control of viruses. More testing is needed to identify who is infected and who needs to be isolated. Countries like the USA, UK, and France have increased their testing capacities. Any form of the testing is vital and will provide more information to tackle this pandemic.
Last reviewed at:
11 May 2022 - 7 min read
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