The national capital registered 4,432 new cases of the coronavirus disease (Covid-19) on Thursday, even as the number of more accurate RT-PCR tests fell again below the 10,000 mark despite high daily tests in the city.
The city also reported 38 deaths on Thursday, which is the highest in 63 days, bringing the total number of people who have died in Delhi to 4,877. The capital’s total infection count is now 234,701.
To be sure, daily tests in Delhi have tripled over the past month, according to data shared by the Delhi government.
The surge in evidence came after Delhi Prime Minister Arvind Kejriwal held an emergency meeting in the last week of August to address the resurgence of cases in the city. The CM had said that the government would at least double daily tests to 40,000 per day. Delhi has conducted nearly 58,000 tests a day on average for the past seven days. A month ago, this number was around 17,000.
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However, much of this increase in testing is due to the increasing number of antigen (or rapid) tests, while RT-PCR tests have not increased as much.
According to Thursday’s bulletin, of the total of 60,014 tests in Delhi, only 9,564 were RT-PCR. This is in line with the general trend for RT-PCR tests over the past week: on average, 9,490 RT-PCR tests have been performed every day in this time period. Only 16.7% of all tests carried out in the last week have been RT-PCR. A month ago (when the tests had not risen to this level) this proportion was higher than 30%.
On Wednesday, the Delhi High Court had asked a committee appointed by the lieutenant governor to immediately convene a meeting “by priority” to define a strategy to increase the number of RT-PCR tests.
The RT-PCR test is more sensitive and less likely to give false negative reports than the rapid antigen test, but it is more expensive, requires more time, and requires a properly biosafety laboratory for processing.
Being cheaper, faster and easier to implement in the field, the government has preferred the rapid antigen tests that are now offered in all government mohalla clinics, dispensaries and hospitals.
“When a test is used to diagnose a person, the sensitivity must be high to be sure that the infection is detected. That is why RT-PCR should be the preferred test outside of containment areas. With rapid antigen testing, there is a chance that positive cases will be missed, especially if the person is asymptomatic. The person can then transmit the infection to others, ”said Dr. Lalit Kant, former director of epidemiology and infectious diseases at the Indian Council of Medical Research (ICMR).
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Recent ICMR testing guidelines recommend the use of antigen testing for routine surveillance within containment areas and RT-PCR testing for non-containment areas and hospitals.
“If the rapid antigen test is used for routine surveillance, we know the sensitivity of the test and the margin of error can be multiplied to estimate the number of infections in the population. However, when it comes to diagnosing a person, it is better to be precise … So the RT-PCR test is better for that. Definitely an RT-PCR test should be done if there are any clinical symptoms, ”said Dr. Shobha Broor, former director of the department of microbiology at the Institute of Medical Sciences of India (AIIMS).
“However, it is not practical to expand the RT-PCR test to the current level,” he added.
Even with the large number of tests, the positivity rate (the fraction of samples that test positive among those tested) continues to hover around just over 7%. On average, a daily positivity rate of 7.18% was recorded in Delhi for the past seven days, a decrease from the 8.6% recorded at the end of August. Certainly due to the fact that antigen tests can lose positive results, experts say this may end up artificially lowering the positivity rate.
A positivity rate of 5% indicates that the transmission of the infection is under control.
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