The increased use of RAT has helped the government ramp up testing for early detection and clinical management of infected cases and isolation of contacts. However, ICMR is examining concerns arising over ‘false negatives’ under RAT and RT-PCR remains the ultimate gold-standard test.
While the number of daily Covid-19 tests almost doubled in the last one month, the share of RAT went up by 40-45% by the end of July as compared to just 4-8% in its first week, official data show.
The average number of daily Covid-19 tests increased from 2,40,620 in the first week of July to 4,68,263 in the last week of July, up by 94.6%. However, in the last week, there have been days when more than 5 lakh tests were conducted. On July 30, over 6.43 lakh tests were done in 24 hours, with RAT accounting for 45.68% of these tests.
“There is now an increased tendency to use rapid antigen tests because they are much faster and cheaper as compared to RT-PCR even though that remains the ultimate gold standard test for detecting Covid-19 infection. While there was an urgent need to ramp up testing across the country, introduction of rapid antigen tests have increased the total number of tests by at least 50%,” an official said.
Currently, India is conducting 14,640 tests per million population to detect the infection and this is showing a steady upward trend with rising number of daily tests. Around 24 states and UTs have reported higher testing per million than the national average.
Apart from RT-PCR and RAT, India is also conducting TrueNAT and CBNAAT tests but these comprise a minor percentage of the total when compared with the former. Together RT-PCR and RAT account for more than 90% of the total tests conducted in a day.
Officials say the increased testing is pursuant to the key strategy of “test aggressively, track efficiently, and isolate and treat promptly” followed by the government for Covid-19 management along with the states.
“Effective implementation of this approach has led to ramping up the testing capacity across the country and facilitated widespread Covid testing of people,” an official said.
However, there are continued concerns related to false negatives under RAT and missing repeat tests through RT-PCR to confirm the negatives. The efficacy of the protocol depends on states ensuring the symptomatic negatives are tested and there is a follow-up to check for indications among other negatives. Some experts feel such errors are impacting the positivity rate despite a major increase in total testing.
The ICMR is evaluating accuracy of rapid antigen testing through a mathematical modelling and will analyse if the proportion of false negatives is substantially high.