Concerns over antigen test strategy after Delhi assembly scare

New Delhi:

A total of 381 rapid antigen tests were conducted on legislators, staff members and journalists for the special one-day session of the Delhi assembly held on Monday, according to official data that also said 15 people, including one MLA, were found positive for the coronavirus disease.

Additionally, 92 people, including 29 of the 50 MLAs who attended the session in the 70-member House, took the gold-standard Reverse Transcription Polymerase Chain Reaction (RT-PCR) ahead of the House proceedings, the data compiled by assembly secretariat showed.

All combined, 20 people, including three MLAs, were found to have contracted the infection.

Experts raised concerns after the rapid antigen tests of at least two MLAs — Vishesh Ravi and Parmila Tokas — threw up false negatives, because of which they went on to attend the assembly session on Monday. Later in the day, their RT-PCR results came back positive when they were in the House along with 48 other legislators, including chief minister Arvind Kejriwal.

Although RT-PCR was mandatory for all MLAs attending the session, they underwent the rapid antigen tests on the assembly premises since their RT-PCR results were awaited.

The incident highlighted the pitfalls in the Delhi government’s reliance on rapid antigen tests, which can throw up “false negatives” — or give a negative result for an infected person — in as many as 50% of positive cases. Delhi has been conducting about 80% antigen tests over the past two weeks as it has scaled up testing.

Dr Lalit Kant, former head of epidemiology and infectious disease at the Indian Council of Medical Research (ICMR), said the assembly incident could be a case study for the Delhi government to review its testing strategy.

“The only hope we can have in this case is that the members were made to sit at least six feet apart from each other and that Covid-positive MLAs were wearing their masks…I cannot stress this enough that the rapid antigen test is only a test of choice for routine surveillance in containment zones and screening at the point of entry. In all other situations, RT-PCR tests should be given priority. Merely increasing the testing through rapid antigen tests will not give a true picture of Delhi’s real positivity rate,” he said.

The Delhi government did not respond when asked for a comment on the matter.

Senior officials in the assembly said the secretariat issued a general advisory to all members and staff who were in touch with Ravi, Tokas and Girish Soni, who was found positive in the rapid antigen tests conducted on the assembly premises before entering the House. Soni left the area immediately after that.

“The assembly hall where all the members sat on Monday has been sanitised thoroughly. All the members and officials who came into contact with MLAs Vishesh Ravi and Parmila Tokas have been advised to take adequate precautionary measures. The administration has not mandated anybody to take precautionary actions. So we cannot give a number of people who have gone under self isolation,” a senior official of the Delhi assembly secretariat said, requesting anonymity.

Delhi law and transport minister Kailash Gahlot, who was sitting in front of Tokas, said he was not in self-isolation. “I came to the secretariat and held routine meetings. Adequate social distancing was followed inside the House. So, the risk of being infected is expected to be minimal,” he said.

Ravi and his brother first tested positive in May. And then, his report came positive again on Monday. Though Ravi called it re-infection, a section of scientists have said they are not sure if re-infection occurs and, if yes, in which period.

“I had undergone RT-PCR test at the assembly before the session on September 11 and it came positive on September 14. People say it’s re-infection. Feel fine and so far there are no such symptoms. I have quarantined myself at home,” Ravi tweeted in Hindi.

Certain criteria have to be fulfilled to determine whether a case is truly that of a re-infection, according to Dr SK Sarin, director of Institute of Liver and Biliary Sciences (ILBS).

“One, did the person become negative after the first infection? To establish this, two tests performed seven days apart should return negative. One test is not enough, because even RT-PCR test is not 100% accurate and the sample collection could have been improper. Two, the person needs to have made antibodies against the virus. In every infection, there is a certain percentage of the population that does not develop antibodies despite being exposed to the infectious agent. Third, the genetic sequencing of the virus from both the infections has to be done to establish that they are different strains,” he said.

“If a person tests positive within a couple of weeks of recovering from the infection, it could be leftover viral particles resulting in a positive test. However, if a person tests positive after a couple of months, a re-infection should be considered,” he said.

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