At a time when there is a clamour for more testing to isolate those with severe acute respiratory syndrome corona virus (SARS-CoV-2), experts are divided on the efficacy of the tests.
While one group opines that neither the reverse transcriptase polymerase chain reaction (RT-PCR) nor the serological antibody test has the sensitivity and specificity to detect the virus in just one test, the other says the tests are the only way to know the spread of the virus in the community.
One rationales behind testing is screening, especially when the virus has caused a pandemic, says Rajeev Jayadevan, president, Indian Medical Association, Kochi. The number of RT-PCR tests done at government centres is too low in such a situation, he adds.
The experts are also divided about the range of efficacy of the RT-PCR test – between 35% and 70%. However, they do agree that if the throat swab is taken correctly, the sensitivity can be 60-70%. “We have to do at least three tests to arrive at a confirmatory result,” says pulmonologist Jacob Baby.
Actually, the tests should be done for a swab sample or sputum along with the serological antibody test to get a more accurate picture, says Dr. Baby. But, the whole testing will cost more than ₹4,000.
The catch is in the affordability of such expensive tests that will still not give at least 99% accuracy. Hence, testing the population for SARS-CoV2 does not look a good option. It will be therefore difficult to isolate asymptomatic people with the antibody tests. The present strategy of social distancing, wearing masks, and breaking the chain are definitely more appropriate.
According to immunologist and rheumatologist Padmanabha Shenoy, in a population where the number of people with infection is much less, antibody testing, which has 95% sensitivity, could throw up a number of false positive results, which would give an indication of being falsely immune to the disease. He quotes an article in the Nature which tells about the futility of conducting the antibody test. “As countries are still gathering evidence on the reliability of tests, it will be a while before the tests become helpful,” says Dr. Shenoy.
Antibody tests would be more helpful when the numbers of infection is high, like in New York, but not in Kerala, he says.
N. Vijayakumar, in-charge of the Regional Blood Transfusion Centre, Aluva, says though the serological enzyme-linked immunoabsorbent assay (ELISA) kits are still not available, they could be a better answer in a situation where the community has to be screened.
“They do take more time - about two hours, but 96 tests can be done at a time, hence much cheaper option. The ELISA test will also be more reliable. The only hindrance is that a technical expert should be involved in conducting the test,” he adds.
