Analysis of Covid data shows that the number of daily tests has been falling of late in several states and most are depending mainly on the rapid antigen test (RAT) rather than on the more accurate RT-PCR tests.
Widespread use of RAT, in some cases up to 90% of all tests, has raised fears that a large number of positive cases could be missed. As per the ICMR protocol, every positive report from RAT can be treated as confirmed, but samples that test negative are to be retested using RTPCR.
It is unclear how many states are rigorously following the retesting protocol.
The reason for many states preferring the RAT is that it not only gives results within 30 minutes, it also can be done outside a laboratory setting. However, RTPCR tests results, which are supposed to be available in eight hours but have often ended up taking days because of backlogs, are considered to be the gold standard.
India is currently doing more than 9 lakh tests per day, down from the 11 lakh plus tests which were being done till about a week back. The daily positivity rate or the percentage of samples testing positive has also been coming down steadily since the last week of October. It is currently just 4.2% compared to 9.1% on October 22.
However, even some states that have not seen positivity rates fall have reduced tests. A high positivity rate indicates the need for more testing as more tests could pick up more cases. Among large states, Rajasthan and Delhi have the highest positivity rate of roughly 13%. Delhi has pushed up testing to reach between 2,300 and 2,700 tests per million population, but about 70% of tests are RAT.
Rajasthan has the lowest tests per million in the country, just 211. The state was doing over 25,000 to 28,000 tests per day in October, when its positivity rate was 5.5%-6.5%. The number has now fallen to around 16,500 tests per day though the number of cases too is going up. Rajasthan is using only RTPCR tests, which might explain the difficulty in rapidly expanding testing.
In Haryana too, the positivity rate has been going up and has touched 11.5%, the highest in the last two months, though the number of daily cases dipped over the last few days after steadily rising from the last week of October. In Haryana, 70% of tests are RTPCR.
Kerala is another state with a very high positivity rate of 10%, though this is lower than the peak in the middle of October when it had touched 16%. With the number of tests being done almost the same, the number of cases have been declining since the end of October.
After Delhi, Kerala and Karnataka have the highest testing rates in the country of about 1,500 tests per million, but over 60% of the tests being used in Kerala are the rapid antigen tests. In Karnataka, RAT constitutes only around 32% of the total number of tests.
In Maharashtra, though the positivity rate of 8.5% is high relative to most states, it is much lower than in October when it had reached over 25%. From doing almost one lakh tests daily, the number of tests per day is now around 40,000. Daily cases too have come down from 22,000 plus around the middle of October to less than 4,000 since the beginning of this week. Questions have been raised about the possibility of this reduction being due to increased use of RAT. had reported that in 14 of the state’s 36 districts, 50% of the testing was through RAT. In four of them, 72-83% of the tests were RAT.
States like Bihar, Gujarat and Telangana too are depending almost solely on RAT for their covid testing. While official data was not available in all cases, government sources in each of these states confirmed that around 90% of tests were RAT.