There are several tests that can be used to detect viruses. Each test has its pluses and minuses. There is no such thing as a coronavirus test or a sars-cov-2 test or a covid-19 test.
There is such a thing as viral infection test.
A PCR test, also called an RT-PCR test, is used to detect a wide variety of viral infections.
PCR is polymerase chain reaction. RT is reverse transcription. In order for the PCR test to specifically detect a specific virus, the laboratory must choose and apply a specific primer to your DNA sample.
A test that can find a specific virus fragment of RNA in your DNA is like finding a needle in a haystack of many fragments. Thus there are several limitations as to accuracy and reliability.
Polymerase Chain Reaction (PCR) Limitations:
1. Any form of contamination of the sample by even trace amounts of DNA can produce misleading results. 2. In order to design primers for PCR, some prior sequence data is needed. Therefore, PCR can only be used to identify the presence or absence of a known pathogen or gene. 3. The primers used for PCR can anneal non-specifically to sequences that are similar, but not completely identical to target DNA. [Therefore, the primer used to detect covid-19, might also detect any number of similar viruses, such as common cold, influenza, MERS, sars-cov-1 and others, thus return a false positive result.] 4. Incorrect nucleotides can be incorporated into the PCR sequence by the DNA polymerase, albeit at a very low rate. This ain't even all the limitations.
There are limitations created by the decisions made in the design of the test and how samples are obtained and processed. This is true with any type of test, for example, IQ tests. In order to create a virus detection test, several decisions have to be made as to how much of a presence of a viral RNA constitutes a positive result. What are the baselines, thresholds and levels of specificity the test requires in order to return a true positive result and a true negative result? What is the allowable amount of inconclusive or indeterminant results?
A PCR test can determine whether or not a fragment of a viral DNA exists, but it cannot determine whether or not you are sick or will get sick or whether or not you are infectious (can transmit the disease).The same positive test result will be returned for two different people: even if one person who has just a tiny amount of the virus and is asymptomatic and the other person has a huge amount of the virus and has full blown symptoms.
In order for PCR tests to be accurate, a lot has to go right before and during the testing process.All this is to say, we must break the spell of thinking covid-19 tests are so reliable that they become the primary method to determine if infection exists and if infectiousness exists. PCR tests should not be used to inform other decisions as to how to deal with this particular virus. Covid-19 tests, as they are being called, are a mean means to a mean end to the little bit of life and liberty we have left. What tests could potentially be used for the screening, diagnosis and monitoring of COVID-19? A Covid-19 test by way of a PCR test that returns a “positive” result that the virus particle was detected does not mean you are infectious contagious.
In order for PCR tests to be inaccurate, only one thing has to go wrong.
