Rapid test reliance may slow Covid 19 fight.

NEW DELHI: Across the country, Reverse transcription-polymerase Chain Reaction (RT-PCR) tests, considered by experts and authorities as the “gold-standard” for tests, remain the preferred method of testing accounting for nearly 60% of samples tested in the 15-day period between August 2 and August 15.

Testing for the coronavirus disease (Covid-19) in Delhi has become heavily reliant on antigen tests, which experts say are not as reliable as RT-PCR tests and end up skewing crucial data that could hamper the fight of the city to contain the virus. At least seven of every 10 tests conducted is an antigen test.

High dependence on antigen tests, which throw up more false negatives (they identify infected people as uninfected), leads to two major problems – under-detection of cases and tilting data metrics such as positivity rate and case distribution.

There has been a slow rise in daily cases in Delhi over the past three weeks -- from a weekly average of 997 daily in late July to a current weekly average of 1091 daily cases. And while the positivity rate is well off its June peaks of 30%-plus, it has risen from around 5.7% in late July to around 6.6% now. On Wednesday, Delhi registered 1,398 cases. To be sure, the situation in the Capital is far better than it was -- and also among the best in the country (especially in a large urban area). Across the country, Reverse transcription-polymerase Chain Reaction (RT-PCR) tests, considered by experts and authorities as the “gold-standard” for tests, remain the preferred method of testing accounting for nearly 60% of samples tested in the 15-day period between August 2 and August 15, according to an HT analysis. Click here for complete coronavirus coverage

average of 1091 daily cases. And while the positivity rate is well off its June peaks of 30%-plus, it has risen from around 5.7% in late July to around 6.6% now. On Wednesday, Delhi registered 1,398 cases. To be sure, the situation in the Capital is far better than it was -- and also among the best in the country (especially in a large urban area).

Across the country, Reverse transcription-polymerase Chain Reaction (RT-PCR) tests, considered by experts and authorities as to the “gold-standard” for tests, remain the preferred method of testing accounting for nearly 60% of samples tested in the 15-day period between August 2 and August 15.

The biggest advantage of antigen tests is that they provide results within the hour and are relatively cheap. These kits are designed to detect antigens (substances in human bodies that stimulate an immune response) and can be performed in mobile stations and do not necessarily need labs. But the downside is that they have a far higher chance of returning false negatives, and thus can let cases slide under the radar. When time is a constraint, and test results are needed almost in real-time, there is nothing as good as an antigen test although rapid molecular tests such as RT-PCR ones are being developed.

The real-time reverse transcription-polymerase chain reaction (RT-PCR) is the most definitive test available. It is used for the detection of nucleic acid from Sars-CoV2 and is based on PCR, a process that duplicates and amplifies genetic fragments of the virus so that these become easily detected

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