Covid-19: What you need to know today
Delhi’s administrators, who continue to rely overly on antigen tests (last week, these accounted for 83% of the total 397,722 tests conducted), couldn’t have asked for a better demonstration of their (the tests’) inaccuracy, and how the erroneous results could, in turn, have cascading implications.Updated: Sep 16, 2020 07:10 IST
In Dispatch 156, I wrote about why it did not make sense to use rapid antigen tests all the time, or be overly dependent on them — like Delhi continues to be.
To recap, such tests give out too many false negative results (identifying an infected person as uninfected) to be reliable. And the protocol in place (which, to make things worse, isn’t strictly followed by anybody) of ensuring symptomatic individuals who test negative in a rapid antigen test are administered a molecular test such as the RT-PCR one as a follow-up is pointless — at least 40% and as high as 80% of those infected with Sars-CoV-2, the virus which causes the coronavirus disease (Covid-19), are asymptomatic.
Sure, there is a context in which it makes sense to use rapid antigen tests. After all, they provide results within the hour, as compared to the minimum of 24 hours it takes for an RT-PCR test (and in practice, with logistical delays and backlogs, this goes up to three to four days sometimes). So, in containment zones, in airports and railway stations, and ahead of public events (such as the JEE and NEET entrance examinations; no test was administered the candidates, frittering away a great opportunity to test a large number of people) — wherever time is a constraint — it makes sense to use rapid antigen tests. And sure, it makes sense to ensure that a follow-up RT-PCR test is administered to symptomatic individuals testing negative in an antigen test.
I have previously suggested a hack that could make antigen tests more accurate — two tests administered in parallel to two samples from the same patient (if there is a discrepancy between the two results, a molecular test is administered). This reduces the chances of a false negative by half.
Finally, I have also written about new rapid antigen tests (one was launched by Abbott Laboratories, but only in the US recently), which are fast, inexpensive, and as accurate as molecular tests. We must get those. At the time of writing the column referred to in the first instance — it also mentioned Uttar Pradesh and Bihar, two other states overly dependent on rapid antigen tests — I did not expect that an opportunity to use a real-life example to explain why such tests shouldn’t be used indiscriminately would present itself in a few days. The math presented in that column was simple, but because it concerned a hypothetical situation, administrators in Delhi, Lucknow and Patna may have missed its import.
And so, with that elaborate prelude, let’s look at Exhibit A: The Delhi assembly.
This is what we know: 50 lawmakers attended the Delhi assembly’s special one-day session on Monday. All of them had previously taken RT-PCR tests, but not all the results had come in by Monday morning. A rapid antigen test was administered to these lawmakers. It isn’t immediately clear how many were administered the test. It was also administered to assembly officials and journalists covering the session. One MLA tested positive and was immediately sent into quarantine. The others tested negative, and the session began. The positive RT-PCR results of two MLAs came even as the session was in progress — they left the assembly immediately, but, by then, their colleagues had been exposed to them. While all 47 of them have tested negative, they have shared a closed room (a large one) with the two lawmakers, should ideally go into quarantine, and have themselves tested after five days (if they are infected, it will show up by then).
Delhi’s administrators, who continue to rely overly on antigen tests (last week, these accounted for 83% of the total 397,722 tests conducted), couldn’t have asked for a better demonstration of their (the tests’) inaccuracy, and how the erroneous results could, in turn, have cascading implications. Delhi chief minister Arvind Kejriwal was in the House at the time, although it isn’t clear whether he came in contact with the infected lawmakers. A mere greeting, or passing an infected person in the corridor, is unlikely to be dangerous — the infection comes from prolonged exposure. But, building on several research studies, a bunch of talking heads in a room are more at risk than a bunch of silent ones.
I hope those plexiglass partitions in Parliament are tall enough.