Ever since the start of the Covid-19 pandemic, many have reiterated the call for the government to intensify its Covid-19 testing capabilities. As more people became exposed to the virus at the start, testing became paramount to determine if an individual was exposed to the virus so that the appropriate medical action could be taken.
Though vaccines offered a level of protection against Covid-19, it is not yet complete. Vaccines still do not offer treatment so testing should continue despite the presence of vaccines, experts insist. Truly, more comprehensive and effective testing schemes were developed but for some, its irrational use may lead to further agony, wherein testing was done but not needed, or not done when it is needed.
“Covid-19 testing: May Nagbago ba?” was the title of the most recent webinar, the 79th episode, organized by the University of the Philippines under its “Stop Covid Deaths” series, where they had Dr. Raul Destura, professor at the UP College of Medicine, director of the National Training Center for Biosafety and Biosecurity University of the Philippines Manila National Institutes of Health and an outstanding Filipino scientist, as lead presenter.
He illustrated the Covid-19 testing platforms that have been developed since the onset of the pandemic, which ones are appropriate for testing, and which ones are usable for other areas.
He emphasized on how diagnostic technologies can be useful, and which type of analytical samples are useful in identifying the right technology for the right sample. Dr. Destura mentioned that Polymerase Chain Reaction (PCR) technology does not discriminate between live and dead viruses. “It is still important that whenever we see test results, we ask our doctor about it to get the appropriate interpretation based on clinical presentation in relation to onset of symptoms and host’s condition. Do not rely on the test right away.”
He said PCR positivity and viral viability are two different entities in interpreting infectivity, and PCR positivity alone may not be enough to make decisions on whether one is infectious or not from a clinical standpoint. However, he said that from a public health standpoint, sometimes the interpretation may be different because public health risk mitigation is now included, that some decisions are applicable for public health control, while some decisions need patient-based interpretation by the attending physician.
Dr. Destura also explained that for test results to enable a specific clinical decision, test developers, policymakers and clinicians need to consider each of the diagnostic use cases with respect to the intention of testing and the population being tested.
“The timing of the diagnostic testing in relation to the infection is critical in the utility and accuracy of Covid-19 diagnostics,” he said.
Testing platforms available
Right now, there are three major platforms in terms of Covid-19 diagnostics – Molecular testing (nucleic acid testing and antigen testing); Serological testing (antibody testing); and Non-Invasive procedure (Computed Tomography).
He mentioned that in terms of Serological testing, higher quality clinical studies assessing the diagnostic accuracy of serological tests for Covid-19 are urgently needed. “Currently, available evidence does not support the continued use of existing point-of-care serological tests for acute case detection.”
Dr. Destura also pointed to an ongoing detection technology now, the “cPass SARS-CoV-2 Neutralization Antibody Detection Kit” which indirectly measures neutralizing antibodies. However, there are still challenges, and Dr. Destura pointed out that even the developer of the technology, GenScript, said in an article that customers “should not interpret the results of this test as an indication or degree of immunity or protection from reinfection.”
For Molecular Testing, it all starts with the collection of samples, which should be done correctly at the collection stage, he emphasized. Locally, the one that gained more recognition is the “sequencing” technology, which can be into two sequencing platforms, the “sequencing by synthesis” and “nanopore sequencing,” which involves tedious preparation. In terms of analytical performance of PCR-based studies, he said that based on 13 studies that involved 2,255 individuals, the average sensitivity was at 95.2 percent while average specificity was at 98.9 percent. For the analytical performance of antigen tests based on eight studies involving 1,180 individuals, average sensitivity was at 56.2 percent while average specificity was at 99.5 percent.
“This means if the result is positive, it is 99.5-percent sure that there is Covid antigen in the body. If negative, there’s still a chance that the person may still be positive that’s why patients are advised to wait it out if symptoms will develop or not,” says Dr. Destura.
He pointed out that RT-PCR remains the gold standard for Covid-19 testing, while Antigen testing, though limited by low accuracy, remains as a promising cost-effective platform for population-wide mass screening and point-of-care use.
However, Dr. Destura pointed out that among the diagnostic platforms that exist, choosing what to use depends on the availability, diagnostic accuracy and timing of infection. There are also novel diagnostic techniques that are being introduced, he said, but the use of these technologies depends on regulatory policies which, at present, are still inadequate.
Finally, test developers, policymakers and clinicians should have multi-dimensional points of view, views that include the technicality of the test, the population to be tested, the intention for testing, and the regulatory monitoring of tests.