Testing for the novel coronavirus is the foundation for treatment and infection prevention measures. With the characteristics of various tests in mind, it is necessary to accurately grasp the actual state of infection.
A basic method for checking for viral infections is PCR (polymerase chain reaction) testing. A tool like a cotton swab is used to collect a sample from the inner part of the nose and analysis equipment is used to determine the existence of a virus. The accuracy is relatively high. On the other hand, there is a disadvantage in that it takes time to obtain results because the work requires great care.
Inspections failed to keep pace at the peak of the outbreak, forcing the government to call for reinforcements. Now that the infection situation has settled down, the number of tests has decreased, but the ability to test for the virus should be maintained in preparation for another possible outbreak. From June 2, saliva can be also used as a specimen for PCR tests. It is desirable to use this in an active manner.
Antigen testing plays a complementary role to PCR testing. Inspection kits are used that react with an antigen, in this case a virus-specific protein. Analysis equipment is not required and results are available in about 30 minutes.
It is supposed to be used when emergency patients are brought to hospitals. Although its accuracy is lower than that of PCR tests, it is easier to take measures to prevent infection because the results can be obtained immediately. It is necessary to use tests effectively depending on the situations.
Many people infected with the novel coronavirus are believed to be asymptomatic or show very mild symptoms. Only counting the number of people who test positive through PCR or antigen tests does not provide a real picture of the spread of infections.
In order to do so, using antibody testing is effective. Blood is checked to judge whether antibodies have developed and a history of past infections can be determined. Starting from June, the government began a random sampling of 10,000 people in Tokyo, Osaka and Miyagi prefectures to determine what percent of the population has already gained immunity to the virus.
In New York City, the most affected place in the United States, it was reported that antibody testing found that about 20% of residents had previously been infected with the virus. In effect, coronavirus cases numbering several times higher than the officially announced totals had been hidden from view.
This trend will perhaps be similar in Japan. If antibody tests reveal the detailed infection situation of each region and industry, it will be a major criterion for deciding on the strategy hereafter.
It is inevitable, however, that each test to a certain degree will make a wrong determination. In particular, the performance of antibody testing kits varies. It is said to be appropriate to use such tests to get a sense of the overall trend, rather than using them to reassure those who are anxious about infections.
Everything about the properties of the novel coronavirus has not been understood. Even after people are confirmed through testing to have antibodies, it remains unclear if that will prevent them from being infected again.
In addition to clarifying the actual state of the disease, it is important to make efforts to improve the accuracy and speed of each test in preparation for another outbreak.
-- This article appeared in the print version of The Yomiuri Shimbun on June 3, 2020.
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