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COVID-19 TESTING

       SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) is the virus that causes COVID- 19. COVID-19 is the name of the disease caused by SARS-CoV-2 and not the name of the virus.  “CO” stands for corona, “VI” for virus, “D” for disease and “19” for 2019. The International Committee on Taxonomy of Viruses (ICTV) announced SARS-CoV-2 as the name of the virus causing COVID-19 in February of 2020.  This name was chosen because the virus is genetically related to the coronavirus responsible for the SARS-Cov-1 outbreak of 2003. SARS-CoV-2 is a member of a large family of viruses named for the crown-like spikes on their outer surface called spike proteins. The name corona means crown in Latin.

       SARS-CoV-2 uses the genetic material RNA (ribonucleic acid) to make and replicate itself.  RNA viruses are very resilient, replicate easily and have high rates of mutation. RNA viruses replicate in the cytoplasm of the cell. Cytoplasm is a gel-like fluid inside the cell membrane where various chemical reactions occur. Coronavirus spike proteins can easily penetrate healthy cells

       Two types of tests are generally used to identify a SARS-CoV-2 infection. One is a molecular test known as a PCR (polymerase chain reaction) test and the other is what is called an antigen test.  Each test detects a different part of the virus. The PCR test is considered the gold standard test for diagnosing COVID-19.  It is considered very accurate and reliable.

The PCR test:

       The PCR test detects genetic material from a specific organism, such as a virus. This test identifies the presence of a virus at the time you have the virus but may also detect fragments of the virus in your body even after you no longer and an active infection. When this occurs this test produces a false positive which means the test shows you have an active infection when in reality you don't.

       The PCR test for COVID-19 is a molecular test that analyzes a specimen from your upper respiratory tract which is obtained through a nasal swab. This test looks for genetic material such as the RNA (ribonucleic acid) of SARS-CoV-2. It does this by amplifying the genetic material to identify if SARS-CoV-2 is present. Here is how it works:

       PCR technology is used to convert small amounts of RNA from the nasal specimen into DNA (deoxyribonucleic acid). The DNA is mixed with a solution containing an enzyme called a polymerase and then heated. This causes the DNA to separate into two single-stranded DNA pieces. The heat is then lowered and a piece of DNA called a primer is used to bind to the DNA strands and copy them. The DNA primer guarantees that only SARS-CoV-2 DNA is identified. This process is replicated many times until billions of copies are made of the SARS-CoV-2 DNA.  A fluorescent dye is added to the material being produced by this process which is then read by a machine to determine the presence or absence of SARS-CoV-2.

       This is a very sensitive test in that it can identify the very smallest presence of SARS-CoV-2 in the body.  This is why you can test positive for COVID-19 even if you have no symptoms.  Because this test involves a number of steps, it usually takes several hours or more to know the results from the time the nasal swab is taken and the test is completed. This test must be administered at a health care facility that has the wherewithal to process the test.    

The Antigen Test:  

       Antigens are anything that causes the body to produce an immune response.  When a substance enters the body that is foreign to the body, it often triggers the release of antibodies which are designed to attack and destroy the antigen. The antigen test for the SARS-CoV-2 virus uses lab-made antibodies to search for the antigen SARS-CoV-2.

       Like is true with the PCR test, a nasal swab is taken to collect material from your upper respiratory tract. This material is them treated with a liquid containing salt and soap that breaks apart cells and other particles. This liquid is then applied to a test strip that has antibodies of SARS-CoV-2 painted on a small thin line that appears on the strip.  

       Just as is true of antibodies in your body attaching themselves to antigens, the antibodies on the test strip will bind to the antigen SARS-CoV-2 if it is present.  If the antibodies bind to the SARS-CoV-2 antigen, a colored line appears on the test strip indicating the presence of SARS-CoV-2 (a positive test). If the test strip remains colorless, the test has not identified SARS-CoV-2 (a negative test).    

       Antigen tests are not as sensitive as the PCR test.  If a person has a lot of SARS-CoV-2 in their body the antigen test will be very accurate in identifying the present of this virus. However, if a person has a small amount of the virus in their body the antigen test may not pick up on it.  The antigen test doesn’t amplify the virus like does the PCR test. So there needs to be enough of the SARS-CoV-2 antigen in the nasal swab in order for the antibodies on the test strip to generate a response. In the early stages of a SARS-CoV-2 infection, not enough of the virus may be present in the nasal material to produce an immune response.  If this is the case, the antigen test may produce a false negative which means you have an active infection of the virus but the test shows you don't. 

       What is attractive about the antigen test is that the results can be obtained in less than 15 minutes and these tests can be administered by anyone. These are the kind of tests administered at public events where there is believed to be a need to determine the presence or absence of SARS-CoV-2 infection.  Antigen test kits are available at low cost at most Pharmacies.