Asking for “strict compliance”, Chief Minister Arvind Kejriwal Wednesday said symptomatic people who test negative during a rapid antigen test (RAT) must be retested using RT-PCR. This came after he held a meeting with health department officials on Wednesday morning.
“Existing guidelines say that if any patient’s antigen test is negative but has symptoms, RT-PCR test must be done on him. I directed officers today to ensure strict compliance of these guidelines,” he tweeted.
As per Delhi Health department data, between June 18 and July 29, 4.78 lakh rapid antigen tests were carried out. Of these, over 3.9 lakh were conducted from July 1-July 29. The number of RT-PCR tests conducted in this period were 1.8 lakh, less than half of rapid antigen tests.
Till July 23, 2,818 people (showing symptoms) were re-tested through RT-PCR method, of which 404 tested positive.
Rapid antigen tests, which provide results within 30 minutes, started in Delhi on June 18. While the sensitivity of RT-PCR tests is 70%, that of antigen tests is 40%. This is why ICMR advises governments to make symptomatic patients undergoing RAT and testing negative to get re-tested through RT-PCR.
While sensitivity of antigen tests is lesser, they are helpful in expanding testing at a faster rate, especially in containment zones, health centres and among special surveillance groups prone to getting infected.
On Monday, the Delhi High Court had asked the Delhi government why it was going with rapid antigen testing, which has a higher rate of false negative results as compared to RT-PCR, as the primary mode of Covid testing. “Should we go by RAT at all, instead of RT-PCR?” a bench of Justice Hima Kohli and Justice Subramonium Prasad had said.
The National Centre for Disease Control (NCDC) has also written to the Delhi government to increase testing through RT-PCR. A sero-survey conducted by NCDC recently found over 23% Delhi residents have developed antibodies against the infection.
Dr Lalit Kant, former head (Epidemiology and Communicable Diseases Division), ICMR, told The Indian Express: “Rapid antigen test is high on specificity and low on sensitivity, and can give false negatives. If a person has symptoms and tests negative by rapid antigen test, then he/she should be tested by RT-PCR. This is based on the fact that sensitivity of RT-PCR is higher than that of rapid test. Sensitivity is the probability that a person with disease tests positive. What we do not know yet is how infectious is a person who is rapid test negative and RT-PCR positive. Research on this would be useful for refining testing strategies.”
At rapid test centres, those who test negative are handed out small slips of paper, bearing the words “this is to certify that Mr/Ms NAME has not tested positive in the Rapid Diagnostic Test for Covid 19… if you are symptomatic, then you must continue to isolate yourself and get an RT-PCR test done as this test does not rule out Covid-19 infection” in English.
On Wednesday, the city saw 1,035 new cases and 26 deaths. The total case load is now 1,33,310 and the death toll stands at 3,907.
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