Developments in Rapid Testing

As businesses, schools, and workplaces continue to reopen, rapid testing is a pressing need in order to effectively control the spread of COVID-19 and cut chains of transmission. The average wait time for test results in Texas is 4 days and a recent nation-wide survey shows that nearly 40% of Americans have to wait more than 3 days for results, undermining public health measures. 

Bottlenecks in testing accessibility and scalability can be caused by diagnostic assay costs, complexity of test, and supply chain shortages. In order to overcome these issues, researchers at Yale School of Public Health developed SalivaDirect, a cost-effective and flexible protocol which requires fewer reagents, utilizes a RT-qPCR assay, and was validated with reagents and instruments from multiple vendors to minimize the risk of supply chain issues. The test was found to have 94% agreement with naso-pharyngeal tests (Vogels et al. 2020). The cost per sample, which for traditional methods of testing is $100 on average, is a maximum of $4.37. This protocol has received an EUA for use at CLIA certified laboratories.  

A saliva test also recently received EUA for self-collection. Unlike SalivaDirect, the CRL Rapid Response test is a kit which can be purchased by entities such as businesses, schools, and nursing homes for specimens to then be mailed to Clinical Reference Laboratories for testing. Although this test does not provide results at point-of-care, expansion of self-collection tests can be useful for surveillance testing in various settings. 

Although the effectiveness of saliva specimens for testing asymptomatic individuals was previously unclear, a study conducted by researchers at the Hokkaido University Graduate School of Medicine in Japan, posted as a preprint on August 15, 2020, indicates that the viral load was equivalent between NPS and saliva samples in asymptomatic individuals and that both are useful in detecting viral RNA. The study included 1,924 individuals and is the first to pair NPS and saliva samples in asymptomatic individuals. Results indicated both nasopharyngeal and saliva specimens had high sensitivities of 86% and 92%, respectively, with specificities greater than 99.9% (Yokota et al. 2020). 

A third antigen test, LumiraDx SARS-CoV-2 Ag Test, received an emergency use authorization this week and can be used in point-of-care settings. Although this test utilizes nasal swabs, it does not require RT-PCR technology and produces results in 15 minutes. The test has a sensitivity of 97.6% (81/87) and specificity of 96.6% (168/170). Because the amount of antigen in a sample may decrease as the duration of illness increases, the test is intended for use within the first 12 days of onset of symptoms. 

Overall, the developments in saliva-based nucleic-acid tests and rapid antigen tests is a positive step forward in making COVID-19 diagnostic testing more accessible and scalable.