Delhi Covid-19 testing down from high; antigen dominates

Testing for the coronavirus disease (Covid-19) in Delhi in recent weeks appears to have again dropped from peak levels, shows Delhi government data.

Delhi conducted 59,368 daily tests at an average for the week ending September 20, what has been the city’s highest recorded rate of testing till date. Since then, this number has seen a near-consistent drop. Two weeks ago, the city conducted an average of 54,629 tests per day, and this has further dropped to 50,116 in the past week — down by around 16% from the peak.

This drop in testing has largely coincided with the drop in new cases in the city. The seven-day average of daily cases has dropped from 4,174 for week ending September 17 (the peak so far) to 2,702 in the last week — a drop of 35%.

In late August, taking note of persistently rising Covid-19 numbers at an emergency meeting, the Delhi government had decided to massively scale-up testing in an effort to catch and isolate more infections. As a result, the number of tests during this period had gone up from under 20,000 to over 60,000 by the third week of September.

Experts said the government should not lower its guard on testing and should be conducting as many tests as possible.

“Even if there are fewer cases, the number of tests should not be reduced. You should do as many tests as possible; there is no upper limit. If a large number of tests are being done and very few cases are detected, then the government will know for sure that there are very few cases in the community. However, if only a small number of tests are done there is a possibility that we might be missing the cases,” said Dr Lalit Kant, former head of the department of epidemiology and infectious disease at the Indian Council of Medical Research.

Experts also questioned the Delhi government’s strategy of relying heavily on rapid antigen tests to increase testing numbers instead of the gold-standard RT-PCR test.

Rapid antigen tests were introduced Delhi in mid-June to scale up testing when the number of cases had started shooting up. The downside of antigen tests is that they tend to give anywhere between 50-80% false negatives, or in other words, they can miss positive cases. This is the reason, anyone with symptoms such as fever, cough and sore throat who tests negative using the rapid test is asked to undergo an RT-PCR test.

“Rather than the rapid antigen test, the government needs to scale up RT-PCR test that are more accurate at picking up infections. There are clear ICMR guidelines on where the tests should be used and the same strategy should be followed. Currently, very few of the rapid tests are being re-checked using RT PCR; all the people who have any symptoms should ideally be retested using RT-PCR,” said Dr Kant.

This will help in monitoring the increase and decline in the cases that might happen over the next few months.

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