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What is a PCR test?


We often hear the term PCR test in reports about COVID-19 (new coronavirus infection disease). Some say it is better to take one, even for asymptomatic (without symptoms) people, while some specialist physicians disagree.

Such a difference in opinions leads to more anxiety. It vitally important in the battle against COVID-19 for each person to have the correct knowledge. So, I will explain the meaning of the PCR test here in simple terms.

PCR stands for Polymerase Chain Reaction. Polymerase is the name of an enzyme which is effective when genes (DNA or RNA) amplify in our cells. Viruses are very small, so they slip through the usual testing methods. PCR makes copies of a part of the genes of a particular virus in large quantities so that existence of the virus can be confirmed.

The gene of SARS-CoV-2 (new coronavirus) is not DNA but RNA. By scraping mucus from the mouth or nose with a swab and testing with the PCR method, infection by the virus can be determined.

A positive result of the PCR test means infection by SARS-CoV-2. If there are symptoms of fever, cough or pneumonia, the patient should be hospitalized immediately. Some people test positive even though there are no symptoms. Such cases are called asymptomatic infection (subclinical infection) where no symptoms are manifested even though the patient is infected by the virus. Some remain completely asymptomatic until they are cured. Others develop symptoms as time goes by. People who test positive are potentially infectious regardless of the current condition of symptoms. Therefore, we can suppress the infection by isolating such people in hospitals or at home. The opinion of widely administering PCR tests including on asymptomatic people is based on this idea.

At this point, a lot of people would think "We should do PCR tests right now. Why are some experts opposed to testing?"

In reality, administering PCR tests on a lot of asymptomatic people and finding positive people will not end the situation. As I said above, there will be the need for hospitalization. We do not know the number of asymptomatic and positive patients but filling up hospital beds with large numbers of asymptomatic patients may occur when the number of tests increases. Already beds are filling up with moderate to severe patients in hospitals in metropolitan areas. If asymptomatic patients fill up the beds, it will lead to acceleration of the collapse of the medical system. Therefore, we have to provide facilities for asymptomatic and positive patients before enlarging the number of test subjects for asymptomatic people. The sad reality is that we are not prepared yet. Some are of the opinion to keep asymptomatic and positive patients at home as self-quarantine. However this involves the possibility of spreading infection among family members, so it is not realistic.

In addition, PCR tests are carried out by medical personnel. Coughs and sneezes tend to be encouraged when collecting samples through scraping on membrane in the mouth or nose. There is a risk of spreading infection among medical staff even if they are taking proper protective measures. The number of patients is expected to increase. In order not to bring on the collapse of the medical system through shortages of medical facilities and personnel, we need to avoid the risk of medical staff becoming infected. In Germany, PCR tests are widely done by a drive-through method, etc. Collapse of the medical system has not occurred in Germany, but it is risky to simply compare Germany with four doctors per 1,000 and Japan with two doctors per 1,000.

What we should do in Japan is to quickly secure a sufficient number of facilities where mild and asymptomatic and positive patients can be accommodated temporarily. I think we can enlarge the scope of PCR tests to asymptomatic people starting with medical staff including doctors and nurses and caretakers of elderly and hospitals, etc. only after such preparation is completed.


sakakihara_2013.jpg Yoichi Sakakihara
M.D., Ph.D., Professor Emeritus, Ochanomizu University; Director of Child Research Net, Executive Advisor of Benesse Educational Research and Development Institute (BERD), President of Japanese Society of Child Science. Specializes in pediatric neurology, developmental neurology, in particular, treatment of Attention Deficit Hyperactivity Disorder (ADHD), Asperger's syndrome and other developmental disorders, and neuroscience. Born in 1951. Graduated from the Faculty of Medicine, the University of Tokyo in 1976 and taught as an instructor in the Department of the Pediatrics before working with Ochanomizu University.
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