Rapid antigen tests have a specificity around 0.7 while RT-PCR at 0.3 when capturing infectious virus is the goal. “during screening of conditionally healthy people, as well as monitoring those quarantined, rapid tests show significantly better results.”
The search for effective methods to detect patients who excrete a viable virus is one of the urgent tasks of modern biomedicine. In the present study, we examined the diagnostic value of two antigen tests BIOCREDIT COVID-19 Ag (RapiGEN Inc., Korea) and SGTI-flex COVID-19 Ag (Sugentech Inc., Korea) for their diagnostic value in identifying patients who excrete viable SARS-CoV-2. As part of the study, we examined samples from 106 patients who had just been admitted to the hospital, who had undergone quantitative RT-PCR and assessment of viability of SARS-CoV-2 using cell culture. Sensitivity was 0.786 (0.492–0.953) for SGTI-flex COVID-19 Ag and 1 (0.768– 1) for Biocredit COVID-19 Ag. Specificity of rapid tests was significantly higher than that of RT-PCR and was 0.663 (0.557–0.758) and 0.674 (0.568–0.768) for SGTI-flex COVID-19 Ag and Biocredit COVID-19 Ag versus 0.304 (0.213–0.409) obtained for PCR. Thus, for tasks of identifying viable SARS-CoV-2 during screening of conditionally healthy people, as well as monitoring those quarantined, rapid tests show significantly better results.
The SARS-CoV-2 virus pandemic has been a major global problem for over a year. The lack of effective and widely available means of prevention and etiotropic treatment has led to a situation where wearing a mask and social distancing  remain the primary ways to lift pressure off the healthcare system, allowing the most severe COVID-19 patients to receive timely and necessary care in medical institutions, while patients with mild to moderate course are forced to remain on lockdown. At the same time, massive restrictions significantly reduce economic activity and, as a result, increase the risks of slowing down economic growth .
The main problem of monitoring and surveillance of SARS-CoV-2 is the ability of the virus to spread from asymptomatic patients several days before any symptoms occur , . Moreover, contribution to the transmission of the virus from asymptomatic patients and from patients before the onset of symptoms is a significant problem both for the spread of the virus and for accounting for COVID-19 cases .
The recent successful launch of SARS-CoV-2 vaccines gives hope for an early reduction of the pandemic and a return to pre-quarantine living conditions , , , . All major vaccines ensure a convincing level of protection (over 90%) in the short term and reliable protection against the severe course of COVID-19. At the same time, the results of the study do not guarantee protection of those vaccinated from subsequent infection with SARS-CoV-2, an asymptomatic course of the disease, which means that further participation of those vaccinated in the spread of the virus has yet to be investigated. The emergence of new strains capable of partial or complete escape from the neutralizing effect of antibodies poses the most danger during prolonged mass vaccination , , .
Detection of viral RNA does not always mean that a person is an infection carrier and spreader. However, in the light of objective epidemic control, it is important to specifically identify carriers of SARS-CoV-2. Timely and prompt identification of the spreaders of infection and their isolation can improve the effectiveness of anti-epidemic measures. Virus viability, as evaluated using cell culture, for samples with a viral load of 30 cycles (about 105–106 GE/mL and below), in RT-PCR tests, is only 3% . It is obvious that the use of methods to assess virus viability using cell culture is unsuitable for mass use due to the complexity of the procedure and the high cost. This requires the search for new simpler methods to identify the spread of the infection.
Rapid antigen tests, which have recently become widespread for the diagnosis of COVID-19, in contrast to PCR, detect SARS-CoV-2 antigens, which, like RNA, comprise viral particles and are produced in infected cells during the life cycle of the virus. The disadvantage of antigen tests is their lower sensitivity compared to RT-PCR. According to the results of Cochrane meta-analysis, sensitivity varies greatly: average sensitivity is 56.2% (95% CI, from 29.5 to 79.8%), average specificity is 99.5% (95% CI, from 98.1% to 99.9%; based on 8 experiments in 5 studies on 943 samples) . At the same time, the definitive advantage of rapid antigen tests is the significantly less laborious process and the ease of learning the procedure, allowing to use the test at home as Point of Care (POC) testing. The time it takes to obtain the result is also crucial, which can be as low as 5 minutes. Moreover, rapid antigen tests are not susceptible to contamination with amplification products, characteristic of nucleic acid analysis methods, which reduces the likelihood of a false positive result.
To date, there are no data on the effectiveness of rapid antigen tests for identification of patients excreting viable SARS-CoV-2. In this paper, we describe results of the pilot study of two rapid antigen tests BIOCREDIT COVID-19 Ag (RapiGEN Inc., Korea) and SGTI-flex COVID-19 Ag (Sugentech Inc., Korea) for their value in identifying patients excreting viable SARS-CoV-2. As part of the study, we examined samples from 106 patients who had just been admitted to the hospital, who had undergone two rapid tests: quantitative RT-PCR and viability assessment of SARS-CoV-2 using susceptible cell culture 293T/ACE2. Samples were collected from January 25, 2021 to February 8, 2021 at an infectious diseases hospital in Moscow.
More details here: https://www.medrxiv.org/content/10.1101/2021.03.10.21252667v1.full-text