With the number of cases spiking and increased pressure to ramp up COVID-19 testing, the Delhi government began rapid antigen testing as soon as the Indian Council of Medical Research (ICMR) recommended its use first on June 15. But, the ICMR had recommended using antigen tests in tandem with the RT-PCR tests to rule out infections. However, the Delhi government has refused to reveal if it was doing so.
ICMR recommended follow-up RT-PCR tests in case of negative rapid antigen test results because the test kit being used shows a larger number of false-negative cases, according to the advisory released by ICMR. This means that several people who are truly positive for Coronavirus will show negative on the test. The antigen test kit being used in the country has been developed by a South Korean biotechnology firm SD Biosensor and each kit costs ₹450.
The South Korean company stated on its website that the antigen test kit’s sensitivity is 84.3% and specificity I00% after testing the kit on 202 persons under lab conditions. Additionally, they had tested the Korean strain of the virus and not Indian.
However, when ICMR and All India Institute of Medical Sciences tested the kit, it’s accuracy reduced. As per the ICMR advisory, the sensitivity of this antigen test kit ranges from 50.6% to 84% in two independent evaluations. If the test is 50.6% sensitive, it will correctly identify 50.6% of the people who are infected. However, 49.4% of the people who are infected and tested would get a false negative result – they have the virus, but the test results showed that they didn’t. Similarly, if the sensitivity of the test kit is 84%, 16% of those who tested would get a false negative result. So, to completely confirm a person’s negative test result, the person has to be tested using the RT-PCR test kit too.
But since the specificity of the test ranged from 99.3 to 100% at the two sites, all those who test positive through the rapid antigen testing will be positive for the virus. It hardly shows false-positive cases. The specificity of the test will accurately identify people without the disease. If the test is 100% specific, no one will receive a false-positive test result. If the test is 99.3% specific, only 0.7% of those who tested and are not infected will receive a false positive. The rest 99.3% will register true negative. For ease of explanation, we will consider the specificity of this test kit to be 100%.
According to the ICMR advisory, the kit temperature has to be maintained between 2° to 30° C. On June 18, when the rapid antigen testing began in the capital, the temperature was 42° C, the highest in the last one week and a week later, on June 25, the temperature is at 37° C.
ICMR advisory asserts at least twice that suspected individuals who test negative for COVID-19 by rapid antigen test should be definitely tested sequentially by RT-PCR to rule out infection, whereas a positive test should be considered as a true positive and does not need reconfirmation by RT-PCR test. Also, the samples collected have to be tested with an hour as it is stable only for one hour. “Therefore, the antigen test needs to be conducted at the site of sample collection in the healthcare setting. Transportation to the lab is not recommended,” states the ICMR advisory on the rapid antigen testing.
Under pressure, Delhi began antigen testing on June 18, but data for the antigen testing was released only for June 18, 19. Of the 13,074 tests conducted on June 18, 7,040 were rapid antigen tests, the rest were RT-PCR tests. Of these 7,040, 456 tested positive, meaning only 6.5% of those who tested got a positive test result. On June 19, 17,533 tests were conducted. Of these, 12,680 were rapid antigen tests and 951 tested positive through these tests – 7.5% of those who tested.
Since then, the Delhi government has not released separate data. The government had informed the High Court that they had performed 9,356 rapid antigen tests, but beyond that, the government has not been transparent with the testing data.
Moreover, Delhi has not revealed if it is testing those who turned up negative using rapid antigen testing as required by ICMR. This will create a false sense of security in those who tested negative as they could be false negatives. They are likely to spread the disease if they are in reality positive.
The effectiveness of this South-Korean rapid antigen test kit can only be understood if the Delhi government released rapid antigen testing data daily, along with the positive cases. Without the regular release of data, it would be impossible to find out the actual sensitivity and specificity of the test kits. Delhi has begun stating that it has increased its testing numbers and that it would test everyone. The issue here remains that if those tests are rapid antigen tests, then a number of people who are actually positive will test negative. Therein lies the problem.
Why? Let’s consider the case where the sensitivity of the test kit is 50.6% and specificity is 100%. In such a scenario, if 456 persons tested positive through rapid antigen testing on June 18, it also means 445 persons got false-negative reports. Similarly, on June 19, the total number of positive cases identified was 1407 of the total 19,720 rapid antigen tests done. With 50.6% specificity, 1,374 persons got false negatives. In the worst-case scenario, 1,819 persons who tested negative for Coronavirus will be positive.
If the sensitivity of the kit were to be considered as 84% and the specificity still at 100%, on June 18, 86 persons got false-negative test results. On June 19, 267 persons would have got false-negative test results. So, in total 353 COVID-19 positive patients would have tested negative. This is the better case scenario.
Only if the Delhi government released the number of rapid antigen testing numbers and the positives, the economic viability of these kits to carry out these tests on a large scale can be ascertained. Otherwise, the government will have to spend again for testing those who test negative.
Slamming ICMR for not having lab tested the antigen testing on a minimum of 5,000 people before rolling it out, Dr T Jacob John, virologist and former professor at Christian Medical College, Vellore said, “ICMR’s job is to do a multi-centric study on a minimum of 5,000 people to check the usability of the antigen test kits. ICMR has innumerable units in different places. When a test is upscaled, there will be a lot of problems on the field, especially the temperature sensitivity. Let’s be absolutely sure what we want. Even if there is a delay of a few days, nothing will happen. But, do it right. Let ICMR labs do the tests under various conditions and certify that the antigen testing is as good as or better than RT-PCR, then they should go ahead.”
It is under this cloud of uncertainty that ICMR has called for more manufacturers who have developed antigen-based tests, to submit them for validation. They have been asked to provide a minimum of only 300 rapid antigen tests. Additionally, the research institute has been coaxing states to begin antigen testing even without enough trails.
Dr John is questioning the increased use of rapid antigen testing. “ICMR has a state-of-the-art lab. Why aren’t they creating what we need? Why are we using a South Korean test kit in June 2020? What is the urgency and need to do this antigen testing? What is the problem with RT-PCR tests? If the RT-PCR reagents are made in India by the National Institute of Biologicals, the cost price of the test can be approximately Rs 1,000 without profit as overheads are covered by the government. So, why should it cost Rs 2,500. Instead of that we are spending money on the antigen tests. Accuracy is of more importance,” pointed out John.
“Why is everything hush-hush. Why is there such an immense hurry? The COVID-19 outbreak is growing by leaps and bounds. So, now is the time to take calm, collected, and strategic decisions and do it right for once. It’s not the time for trying this and trying that. Why are we confusing ourselves?” John said.