Scientists at Hokkaido University have shown that an antigen-based test to quantify SARS-CoV-2 in saliva samples is quick, easy and cheaper for mass screening.
More than a year after the COVID-19 pandemic began, the RT-PCR test remains the gold standard for detecting the SARS-CoV-2 virus. This method requires trained personnel at every step from collecting NPS (nasopharyngeal swabs) samples to interpreting the results. In addition, the entire process takes an average of 24 to 48 hours. Because the virus can be transmitted from an infected person before symptoms develop, and can even be transmitted from people who are asymptomatic, the ability to screen large numbers of people quickly is critical to controlling and preventing the spread of the pandemic . Faster methods of detecting the SARS-CoV-2 antigens have been developed, but they are not as sensitive as the RT-PCR test. In June 2020, Fujirebio developed a novel antigen-based kit, the Lumipulse® SARS-CoV-2 Ag kit (Lumipulse), to quantitatively measure the viral antigen in biological samples within 35 minutes.
A team of scientists from Hokkaido University used the antigen kit to detect SARS-CoV-2 in saliva samples and evaluated the efficiency and accuracy of the test compared to RT-PCR. Their results show that the antigen detection kit used to perform a chemiluminescent enzyme immunoassay (CLEIA) can detect SARS-CoV-2 in these samples quickly and with good accuracy. The study was published in the journal The Lancet Microbe.
The scientists tested 2,056 people from three cohorts: patients with clinically confirmed COVID-19, people who had contacted patients with COVID-19, and people who were tested on arrival at Tokyo and Kansai International Airports. Saliva samples were collected from all individuals and used for RT-PCR testing as well as CLEIA using Lumipulse. The results of both were compared to determine the usefulness of CLEIA.
The scientists found that CLEIA is a reliable test because it correlates well with RT-PCR. With CLEIA alone, SARS-CoV-2 can be detected within an hour. However, the use of CLEIA for screening and RT-PCR for confirmation increases the accuracy of the diagnosis.
The advantage of using saliva samples is that it is easy to collect: it is quick and can be collected by the people being tested, reducing the risk of healthcare workers being exposed to the virus. In addition, self-sampling of saliva allows multiple samples to be taken at once for quick examination of visitors at large gatherings.
Combined CLEIA and RT-PCR tests have already been carried out on saliva samples in Japanese airport quarantines. The authors recommend using this on a larger scale in order to quickly search for SARS-CoV-2.