Use RT-PCR test to get best results, says govt PDF Print E-mail
Friday, 11 September 2020 00:00
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The surge in Covid-19 infections, to 4.5 million on September 10 from 2.2 million on August 10, has got the government to change its testing strategy. While ramping up testing was, rightly, seen as an important part of the strategy to contain the virus, this did not help as much since the bulk of the ramping up was done by using Rapid Antigen Tests (RAT) which capture about a third of the infections that RT-PCR tests do.

Around 75% of tests in Delhi are now rapid antigen tests, it is 66% in the case of Kerala, and 90% in the case of Bihar. In all these places, infection rates have fallen dramatically after RAT tests rose relative to RT-PCR ones.

In the case of Maharashtra, data released by the government last month found that RAT had missed 23.9% infections. While the rapid antigen test came out negative for 4,235 symptomatic people, subsequently RT-PCR testing found that 1,011 or 23.9% of these persons were Covid-positive.

In Delhi, an RTI filed by The Indian Express reveals that of the 6,054 symptomatic people tested between June 18 and August 27, subsequent RT-PCR testing found 699 or 11.5% were positive.

Similarly, for India, between June 18 and July 21, 15.2% infections were missed by the rapid antigen tests, as per the health ministry.

The ‘case infection rates’ that these daily tests show are dramatically different from the results thrown up by the sero-surveys. In Delhi, while the daily tests show a ‘case infection rate’ of just 10.8%, the sero-survey suggested that 29.1% of the population had Covid-19 at some point, up from 23.5% in the sero-survey conducted in July. And, in the case of Mumbai, while the ‘case infection rate’ is 18.9%, the sero-survey suggested that 33% of the city had been infected by Covid-19. Since the sero-survey is based on a rigorous sampling technique, it is more likely to be representative of the situation on the ground.

Since poor testing allows infected persons – both symptomatic and asymptomatic – to go around spreading the disease, the Union health ministry has asked states to strictly adhere to the ICMR protocol on testing. All symptomatic persons, the ICMR guidelines say, have to be tested with RAT – this gives results within a few hours – but all those who test negative must be tested using RT-PCR protocols as this is seen as the gold standard of testing. “This will also ensure early detection and isolation/hospitalization of such false negatives”, the ministry’s guideline says.

The Delhi government has, on the prodding of the Delhi High Court, gone one step further and said that, if people want to get themselves tested using RT-PCR, they no longer need a doctor’s prescription. While testing protocol have been relaxed over time, till now RT-PCR tests could be done only with a doctor’s prescription. Oddly, though, the Delhi government has said that only 2,000 on-demand sans-prescription RT-PCR tests can be done every day.


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