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Covid-19 Rapid Test Practices

COVID-19 RAPID TEST PRACTICES

Covid-19 has affected more than half part of the world. Many people are in stress situations, various questions arise daily in their minds what if we get infected with the virus? How to treat or cure the virus? Is there any reliable test to detect the virus? 

Coronavirus is a large family of viruses that may cause illness in animals or humans.  In humans, several Coronaviruses are known to cause respiratory infections ranging from the common cold to more severe diseases, such as Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS). The covid-19 has almost triggered in every part of the world creating havoc, taking the lives of millions. The ongoing outbreak poses a challenge for public health laboratories as the outbreak is widespread

“Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so that we may fear less.” 
-Marie curie, Nobel prize winner

With most of the planet under some form of medical martial law, we would do well to follow her advice, understand more, and fearless about the pandemic

In response to growing Coronavirus pandemic, multiple diagnostic test manufacturers have developed rapid and easy to use virus detection devices. Coronavirus testing will help countries managing Covid-19 disease more efficiently before it progresses further.



There are mainly three methods to detect the novel virus; 

  • Genetic/Molecular test
  • Antigen test 
  • Antibody test

MOLECULAR TESTING / REVERSE TRANSCRIPTASE POLYMERASE CHAIN REACTION (PCR)

In response to fast outbreak of covid-19 Molecular testing i-e RT- PCR techniques have been developed to target the covid-19 genes in the RNA strand of the human genome. It is the most reliable test and the first developed, it involves looking after the genetic material of the virus and its amplification to test and trace the Covid-19.

RT-PCR is the Gold standard test for the detection of novel virus. The sample for this test is collected by nose swab of the patient and it is treated with several chemical solutions. The solutions remove substances such as fats and proteins. It only extracts RNA in the sample, the RNA extracted is the mixture of persons own genetic material and COVID-19 RNA (if present). The virus contains genetic material that is +ss RNA.

Molecular testing RT-PCR have generally targeted a combination of following genes;

  • Nucleocapsid
  • Open reading frame (Orf1ab)
  • Envelop
  • RNA dependent RNA polymerase (RdRp)

Mechanism behind the RT-PCR testing

The reverse transcriptase-polymerase chain reaction is a nucleic acid amplification method, converting one copy of DNA is into multiple copies. The Coronavirus contains +ss RNA in the RT-PCR technique, ssRNA is converted into ds-cDNA by Reverse Transcription method by using reverse Transcripts and primer and forms Double-stranded complementary DNA(ds-cDNA). Amplifying the dS-cDNA detected by using a special dye, when the dye binds to DNA if forms fluorescence. 

Fluorescence is measured using a number of cycles by making a graph (i.e. Florescence vs Number of cycles). 

Positive Result
Florescence increased with time and number of cycles and it gives a positive result, this indicates that the patient is Corona positive. 

Negative Result
If there is no change in the fluorescence after one hour, then the test is negative.

PROS of RT-PCR test

  • Entire process is done within a close setup
  • As compared to other viral test detectors RT-PCR has a low level of contamination or errors
  • Most accurate method available for the detection of coronavirus
  • Detect acute infection from the virus
  • Regular testing of health care workers and those employees who are at higher risk of infection could help reduce the transmission.

CONS of RT-PCR test

  • It cannot detect the past infection as the virus is only present for a specific window of time
  • The amplification process takes up to 6-8 hours and a minimum of two weeks for lab results
  • RT-PCR is highly sensitive <60%
  • Requires a health professional to perform the test
  • The sample must be inaccurate volume free from any sort of contamination
  • This test can only be conducted in a lab setting. 


ANTIGEN DETECTION / RAPID DIAGNOSTIC TEST

An antigen is a molecule that stimulates an immune response; it could be proteins, polysaccharides, lipids, or nucleic acids. Each antigen has distinct surface features that are recognized by the immune system.

Antigen detection test detects the presence of viral proteins i-e antigens expressed by the COVID-19 virus in a sample from the respiratory tract. If the target antigen is detected in sufficient concentration it will bind to specific antibodies and detect visually detectable signals within 4-8 minutes. The antigens detected are only expressed when the virus is actively replicating therefore such tests are best used to detect acute infections. Covid-19 has several known antigens, including its nucleocapsid phosphoprotein and spike glycoprotein.

Factors on which results depend;

Time from onset of illness

Concentration of virus in the specimen 

Quality of specimen collected from the person

Precision of formulation from reagents

SENSITIVITY

The sensitivity of this test is expected to vary from 34% to 80% which is not that good. More than half of COVID-19 patients could be missed in such tests depending on the group of patients being tested. It requires further study to detect whether it is accurate or not.

SPECIFICITY

Its specificity is >55%, false-positive results detection may show a person is infected when he/she is not.

PROs of Antigen test

Diagnostic tests must be performed in labs by expert lab technicians.

  • Fast, inexpensive, easier to perform
  • Consume less time than RT-PCR
  • Provides results in 15-30 minutes
  • Nasal swab required for sample specimen

CONs of Antigen test

  • Less accurate with low specificity and sensitivity
  • The targeted amount of virus must be present for the detection
  • High chance of a false-negative result


ANTIBODY DETECTION / RAPID DIAGNOSTIC TEST

The rapid antibody test detects the presence of specific antibody proteins in the blood, serum, and plasma of an infected person, made in response to infections. These antibodies are detected in the blood of people who are tested after infection, their results depicted an immune response to the infection

Antibodies are produced over days to weeks after exposure to the virus. Studies suggest that majority of virus-infected patients have developed antibody response in 2nd week of the infection.

PRINCIPLE

The antibody is made by the immune system in response to a virus entered early in the body. The Coronavirus antibody is the specific antibody and the test kit consists of antibody detection that is IgM, IgG, and IgE. It detects the Antibodies present in the immune system to fight against Coronavirus.

FACTORS ON WHICH ANTIBODY RESPONSE DEPENDS

The strength of antibody response is dependent on the following factors:

  • Age 
  • Type/severity of the disease
  • Nutritional status of the infected person
  • Medication currently being taken
  • Previous infection

PROS of RAPID DETECTION TEST

The rapid test is more efficient and faster, unlike the PCR test which takes up to 2 weeks for results and only provides accurate results during the acute phase of viral infection.

  • Detects proteins that are part of the virus
  • Simultaneous Qualitative detection of IgM & IgG antibodies.
  • Antigen test produces results in minutes
  • The rapid test is fast and inexpensive
  • Rapid test, when conducted over time, can also provide clinicians with more accurate invasion into the disease stage and immunity status
  • RNA extraction and amplification is not required
  • Determines whether an individual has been exposed
  • There is only a 2% chance of detection of a false-negative result

CONS of RAPID DETECTION TEST

  • Diagnosis of COVID-19 based on antibody response will only be possible in the recovery phase.
  • Antibody detection test targeting COVID-19 may also cross-react with other viral pathogens and provide false-positive results
  • A false negative may occur if the amount of SARS COV-2 IgM or IgG is below the detection level.
  • It does not provide the quantity of antibody present.

CONCLUSION

The antibody detection test detects specific IgG and IgM antibodies produced by the immune system in response to the viral infection caused by SARS-COV-2 in the sample of blood, plasma, and serum. Because antibodies are produced for several weeks in order to fight the infection, Rapid Antibody detection test helps to evaluate the pre and post-infection stage and helps to determine whether a person is an asymptomatic carrier of the virus or he/she is contagious and may develop symptoms soon. It could also be used to test almost everyone later during the epidemic in a specific setting to detect who is immune and who is safe to go back to work, to differentiate those who were infected and those who are still contagious. The test detects both the early marker and the late marker simultaneously, IgM/IgG antibodies in whole blood, serum, and plasma samples.  It's fast, inexpensive, and easy to use providing results in a few minutes, unlike PCR which takes 2 weeks to provide results, although critically important RT-PCR is only effective during Acute Covid-19 viral Infection. On the other hand, an Antigen detection test requires the presence of specific viral proteins inadequate quantity of samples to detect the Coronavirus. Antibody/Antigen detection test helps to detect the COVID-19 virus before the person shows symptoms which are extremely important to control the spread of the virus to other people. Industries, businesses, schools, colleges, and universities should test their workers, employees, and students frequently to evaluate and separate the infected person as soon as possible, by setting up a surveillance booth where Rapid tests are conducted twice a week. This would help in decreasing the outspread of Coronavirus in
certain areas or regions.


 

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