There are 7 types of coronavirus that are known to cause infection in humans. Of these, 4 cause mild to moderate disease.
What is PCR Test? How It's Done?
Three other species that have emerged in the last 20 years cause more severe and even fatal diseases:
- SARS-CoV responsible for Severe Acute Respiratory Syndrome (SARS) in 2002 ,
- Middle East Respiratory Syndrome (MERS) MERS-CoV in 2012 and
- SARS-CoV-2, identified in late 2019 by a cluster of pneumonia cases in Wuhan, China .
What are the ways of transmission of COVID-19?
Currently available evidence indicates that COVID-19 can be transmitted from person to person in several different ways. The primary mode of transmission of human coronaviruses is person-to-person contact through respiratory droplets generated by breathing, sneezing, coughing, as well as direct person-to-person contact. Indirect contact with an infected patient is by hand transfer from contaminated surfaces to the mouth, nose or eyes.
Why PCR Test is Performed?
There are three main detection methods for the diagnosis and screening of COVID-19 infection:
- Nucleic acid tests: Detecting the presence of viral RNA it does. Typically these use an amplification step based on RT-PCR (Polymerase Chain Reaction).
- Antigen tests: Detects the presence of an antigen that is part of the virus surface protein.
- Antibody tests: Detects the presence of antibodies produced against SARS-CoV-2.
How to Perform PCR Test? How to Take a Sample?
For those who are suspected of Covid-19 or who apply for screening purposes, a swab is taken from the nose (nasal) and throat (oropharynx). It is advanced to the posterior wall and a swab is taken.
The most widely used method in diagnosis is reverse transcription polymerase chain reaction (RT-PCR).
Different tests detect different regions of the SARS-CoV-2 genome. Some target two or more genes, including the nucleocapsid (N), envelope (E) and spike (S) genes, and the RNA-dependent RNA polymerase (RdRp) gene.
PCR Test How Long Can the Virus Be Detected with ?
Viral RNA spread is higher when symptoms begin and decreases after days or weeks.
- During the course of the infection, detection of viral RNA by PCR has been identified 1-2 days before the onset of symptoms in respiratory tract samples, and may persist for up to 8 days in mild cases.
- Detection of the virus in severe cases. may persist longer, peaking at 2 weeks post-infection.
- Long-term viral RNA shedding has been reported from nasopharyngeal swabs and stool (more than one month after infection in pediatric patients).
- With PCR, the virus can be detected for 10 days or longer after infection. Long-term detection of viral RNA by PCR (15 days or more after the onset of the disease) can be seen especially in immunocompromised patients.
Where and Who Is the PCR Test Performed?
The PCR test is performed in the microbiology laboratory units of the hospitals. PCR testing is also carried out in microbiology laboratories of private hospitals, especially in public hospitals, and in private laboratories with PCR working units. In order for a unit to be able to perform PCR testing and give results, it must have the necessary accreditations and give accurate results, so that the system optimization (we can summarize the replication process as sufficient application of the replication process to the correct gene region) must be made.
Symptoms that may be related to COVID-19. The diagnosis is made by PCR test by taking nasal swab samples from the patients with rheumatoid arthritis. He knows.
How is the PCR Test Result Evaluated? What Does PCR Test Positive Mean?
In real-time PCR method; The signal given by the probes is monitored with the fluorescent dye that increases in proportion to the amount of viral RNA formed. With the cycle number of amplification, a certain amount of virus genome is obtained. Replicated virus RNA becomes traceable by irradiating with fluorescent dye. The molecular weight of the control product is known. Accordingly, the place where the PCR products reach according to their molecular weight is read (the product with the higher molecular weight is left behind) and the test result is reported to be positive or negative.
The person with a positive PCR test is infected with SARS-CoV-2. People in such situations are immediately isolated and the people with whom they have been in contact/past contact are screened to isolate the sick from the society.
Why is the PCR Test Important? Are Its Results Reliable?
- Data comparing the accuracy of the RT-PCR test indicate that the sensitivity of the test may vary by sample type.
- Levels of viral RNA are higher in nasal samples and oral
- The diagnosis of viral RNA in respiratory samples for COVID-19 by PCR supports decision making for clinical, infection control and public health management.
- SARS-CoV-2 detection in the diagnosis of patients with COVID-19-like symptoms is essential for patient care, triage and isolation in healthcare facilities.
- PCR testing is also for contact tracing or asymptomatic infection and disease screening of close contacts.
- PCR screening is also important for the prevention and early control of viral transmission to risky people living in closed institutions such as long-term care homes.
- A positive RT-PCR result for SARS-CoV-2 confirms the diagnosis of COVID-19. Additional diagnostic testing is not required.
- SARS-CoV-2 RNA can be detected in upper respiratory tract specimens weeks after the onset of symptoms in COVID-19 patients. However, prolonged detection of viral RNA does not necessarily indicate continued contagion.
- If the initial test is negative, but the suspicion of COVID-19 persists (such as the presence of symptoms), a repeat test is recommended.
- For repeat testing The optimal time is usually 24 to 48 hours after the first test. It is not recommended to repeat the test within 24 hours.
- The viral load detectable by PCR can be a useful marker for assessing disease severity and prognosis. It has been shown that viral loads in severe cases are 60 times higher than in mild cases.
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