What Is a COVID-19 Test?
Around December 2019, a new type of coronavirus broke out in Wuhan, Hubei Province, China. In February of the same year, infection was confirmed in 31 provinces and spreading rapidly throughout China. At the same time, the infection spread to countries around the world, and by early March 2020, the World Health Organization (WHO) declared a pandemic, with over 4,000 deaths and confirmed infections globally.
The official name for the new coronavirus infection is “coronavirus disease 2019” (COVID-19). It is also caused by a virus named “SARS-CoV-2” by the International Committee on Virus Classification. The coronavirus has swept across the globe, leaving a profound impact on economies and lives.
As of 2021, three types of COVID-19 tests are available.
The testing methods are listed below:
- PCR Test
This is a method of testing for the presence of the virus in saliva or nasal swab fluid. - Antigen Test
This test method detects the protein that is a component of SARS-CoV-2 using an antibody specific to the virus. - Antibody Test
This test is used to determine whether a person has been infected with the virus in the past and to detect an immune response to the virus.
Uses of COVID-19 Tests
There are three types of COVID-19 test methods, and the applicable test differs depending on the specimen used. The main specimens used are nasopharyngeal swab and sputum, in addition to those mentioned for the PCR test.
Below are the results of studies on the efficacy of each PCR test:
The Ministry of Health, Labour and Welfare, and International University of Health and Welfare Narita Hospital have published a study on “Investigation of the usefulness of nasopharyngeal swab and saliva in the diagnosis of new-type coronavirus infection.”
According to this study, the PCR test was defined as (1) the administrative test PCR method using throat swab fluid (public health center) and (2) the test using saliva, and the agreement rate (2/①) was calculated by dividing the positive cases of each method.
For the saliva-based test, the “Infectious Diseases Research Institute method” and “Cobas8800” were used as PCR methods. And “SARS-CoV-2 Direct Detection RT-q PCR Kit“, “2019 New Coronavirus Detection Reagent Kit” and “New Coronavirus Detection Kit SARS-CoV-2 Detection Kit” were used as a direct PCR method. In addition, “Loopamp EXIA” was used as the LAMP method.
As a result, a high concordance rate was observed between “nasopharyngeal swab fluid” and “saliva” in cases within 9 days of onset of illness.
How to Choose COVID-19 Tests
Apart from the previously mentioned PCR method, COVID-19 testing includes ‘antigen tests’ and ‘antibody tests.
There are three types of antigen tests: a qualitative antigen test (simple kit), a qualitative antigen test (laboratory equipment), and a quantitative antigen test.
1. Qualitative Antigen Test (Simple Kit)
The simple kit is user-friendly and suitable for bedside use, with results confirming within approximately 15 to 30 minutes. While the test’s sensitivity is lower than that of the PCR, it maintains a generally high specificity, although some issues have been observed.
2. Qualitative Antigen Test (Instrumental)
Tests using instruments for qualitative analysis demonstrate greater sensitivity compared to simple kits. For instance, sensitivity is approximately 10 times higher when assessing the N antigen quantity. Additionally, results can be confirmed within a similar timeframe as with a simple kit. However, this test necessitates specialized equipment, available in both small and large sizes.
3. Quantitative Antigen Test
The quantitative antigen test is mainly used at airport quarantine stations and is comparable in sensitivity to simple genetic tests, such as the LAMP method.
This test can use saliva as a specimen. It can also be used in asymptomatic individuals. Specificity is generally high.
However, there is concern about the possibility of false-positive results when used in screening populations with low pretest probability (prevalence) (asymptomatic individuals).
4. Antibody Test
The WHO website also states in “Diagnostic testing for SARS-CoV-2. 11 September 2020” that antibody tests should not be used alone for diagnosis because the interpretation of antibody tests depends on the timing of testing during the clinical course.
As of December 2020, there have been no approvals for antibody tests as in vitro diagnostic tests.
Antibody testing implies a high probability of having been infected in the past, and the presence of antibodies in the body does not mean that there is protective immunity to infection. In addition, the human immune response is highly individualized and may be influenced by factors such as age, gender, race, and region of residence.
The clinical significance of antibody testing should be carefully considered when using it to diagnose individual patients.
Trends in COVID-19 Tests and the Number of Infected Patients
The number of COVID-19 tests conducted nationwide was approximately 76,000 PCR tests conducted between February 18, 2020, and May 19, 2022.
As of May 19, 2022, the number of tests that can be performed per day is approximately 405,000.
Of these, the total number of positive cases was 8.55 million up to May 21, 2022.
Regarding the test count, a total of 1.53 million tests were conducted by May 20, 2022, encompassing local health laboratories, private laboratories, and more. This figure is inclusive of both PCR and antigen tests.
Free COVID-19 Test for New Coronavirus
Free COVID-19 testing is conducted by local governments nationwide as a free PCR and other testing program in line with the “General Testing Program at the Time of Infection Spread” (hereinafter referred to as “General Testing Program”) and the “Program to Promote the Establishment of Vaccine Testing Packages and Testing for All Eligible Persons” (hereinafter referred to as “Program to Promote the Establishment of Testing”).
- General Inspection Business
In the general testing program, prefectural residents can be tested free of charge when the governor requests testing of prefectural residents who are concerned about the spread of infection due to the tendency for infection to spread.The people who are eligible for testing include asymptomatic prefectural residents who have no fever or other symptoms and who are concerned about infection or who have reasons for wanting to eliminate their fears of infection.
The implementation period varies from prefecture to prefecture.
- Retention Promotion Project
The program is a free vaccine and testing package, or free testing for all eligible persons and for asymptomatic persons who need to confirm the results when they eat, drink, hold events, travel, or engage in other activities.Those eligible for testing include those who have not received the third dose of vaccine or those who are eligible for all-subjects testing and need to confirm a negative test result for activities such as eating, drinking, events, and travel.
Even if they have already received the third vaccination, they are eligible for the free test if they are asked for the test result when they have contact with the elderly or people with underlying diseases, or when they are subject to the all-subjects test.
The period of implementation is until June 30, 2022.