Field evaluation of Rapid SARS-Cov2 Antigen screening test on self-collected deep throat saliva samples in Malaysia

Low cost Rapid Antigen Tests are widely used in Malaysia and the government has also mandated worksite screening as a condition for reopening. Numerous RAT kits have been approved by the Malaysian Medical Device Authority. However, it remains uncertain how these kits would perform in the field. We enrolled workers between June and September 2021 from 23 worksites. They were trained and experienced in performing RAT selftest by virtue of their worksite participation in routine screening program. These workers also had reverse transcriptase polymerase chain reaction tests in the course of mass screening or contact tracing. We also enrolled patients with PCR confirmed Covid19 from a quarantine centre. These patients were instructed on selftesting and then immediately perform RAT under supervision. Two manufacturers donated RAT for this study. A total of 340 participants were enrolled, 130 were from quarantine centre and 210 from worksites. The overall sensitivity of RAT compared to PCR was 70 percent. The specificity was 91 percent. Sensitivity decreased with increasing PCR cycle threshold values. Sensitivity is also lower among untrained subjects at each level of Ct. Logistic regression analysis confirmed false negative result is associated with Ct and participants prior training and experience. This study shows that in the real world, RAT performance were markedly lower than that reported by the manufacturers. The test sensitivity is dependent on the operator training and experience, as well as on viral load as measured by Ct. User training and repeated testing for screening purpose is necessary to mitigate the low sensitivity of RAT.