The regulations of Rospotrebnadzor, which were in force until recently, prescribed to ensure the coverage of the population with testing-200 tests per day per 100 thousand people-exclusively by PCR. The decree of the chief sanitary doctor, published on March 30, assumes the use of any diagnostic drugs and test systems registered in the country for screening COVID-19.
Earlier, on March 12, the staff of the Gamaleya National Center of Epidemiology and Microbiology posted on the medRxiv preprint server an article The Value of Rapid Antigen Tests to Identify Carriers of Viable SARS-CoV-2, describing the results of a study on the value of rapid antigen tests to identify patients who secrete viable SARS-CoV-2.
The authors studied the diagnostic value of two antigen tests from Korean manufacturers-BIOCREDIT COVID-19 Ag (RapiGEN Inc) and SGTI-flex COVID-19 Ag (Sugentech Inc), they examined samples of biomaterials from 106 patients who had just been admitted to the hospital, who underwent real-time PCR, and in addition, the activity of the virus was tested in cell culture.
The sensitivity was 0.786 (0.492-0.953) for SGTI-flex COVID-19 Ag and 1 (0.768-1) for BIOCREDIT COVID-19 Ag. The specificity of the rapid tests-0.663 (0.557-0.758) for SGTI-flex COVID-19 Ag and 0.674 (0.568-0.768) for Biocredit COVID-19 Ag-was significantly higher than that shown by the PCR method-0.304 (0.213-0.409). Thus, the authors conclude, for the tasks of detecting live SARS-CoV-2 during the screening of conditionally healthy people, as well as for monitoring those who are in quarantine, it is preferable to use rapid tests.
With comparable effectiveness in detecting patients, antigen tests showed significantly fewer false-positive results on samples of patients who no longer secrete a viable virus and, therefore, are safe for others. This, the authors note, suggests that the practical use of antigen tests can reduce the time of isolation and quarantine.
However, the researchers make a reservation, a direct comparison of the analytical characteristics of real-time PCR tests with antigen tests is not entirely correct, since the sensitivity of PCR tests is much higher, but express tests, according to the result obtained, are of great value for identifying virus carriers. It is also important, the authors of the work add, that testing for antigen does not require high-tech equipment, trained medical staff and complex quality control systems, which means that the widespread use of antigen tests for mass screening and identification of persons who secrete the virus among conditionally healthy people is potentially of great value.
The BIOCREDIT COVID-19 Ag test system from the Korean RapiGEN is based on the immunochromatographic analysis of the virus antigen. A swab from the nasopharynx is examined: the taken biomaterial is placed into a special solution, after which 3-4 drops of the solution are applied to the test strip. The test result is shown in 5 minutes. The use of the BIOCREDIT test system was approved by Roszdravnadzor in July 2020. The article is published on VADEMECUM