On Monday, the Delhi High Court asked the government why it is resorting to using antigen tests rather than the "gold standard" PCR Tests. Antigen Tests are globally known to be unreliable as they very often falsely report Covid-infected people to be Covid-free.
In fact, several rigorous medical studies suggest that out of every 100 Covid-infected people, the Rapid Antigen Test reports as many as 60 people as Covid-free and only detects the virus in 40 of the 100 infections.
However, a study of the coronavirus situation in Delhi suggests that there is both bad and good news (even if the reality is not quite as good as the Delhi government is depicting).
1. MORE TESTING: The increasing number of Covid-19 tests in the capital is a positive development: from about 15,000 tests per day a month ago to 21,000 tests a day currently, which is an increase of almost 50% in less than a month. A significant achievement. The real spurt in testing took place in the first 7-10 days of July (since then, unfortunately, there has been a plateauing in the number of tests).
2. OFFICIAL DATA FOR ALL, NOTE ALL, TESTS COMBINED SHOWS THE POSITIVITY RATE FALLING SHARPLY: Along with the rise in the number of tests every day, Delhi also released official data showing a remarkable improvement as reflected in a huge drop in the % positivity rate: from 22% about a month ago to 6% currently. The positivity rate (i.e. the % of people tested who are found to be positively infected by Coronavirus) is a crucial indicator of whether the pandemic is coming under control - i.e. if the positivity rate is high, the virus is spreading faster.
3. HOWEVER ,THIS IS A SOMEWHAT MISLEADING PICTURE. The rise in the number of tests and the sharp fall in the positivity rate is because of a sharp rise in the number of Antigen Tests - the less reliable testing method.
The sharp increase in testing in Delhi was primarily because of a sudden spike in the number of the low-cost Rapid Antigen Tests which went up from under 7,000 tests per day to almost 14,000 tests a day.
Unfortunately, with the rise in the number of antigen tests - Delhi simultaneously saw a decline in the number of PCR tests, the most reliable testing method: during the same period, there was no corresponding increase in the daily number of the more reliable and more accurate PCR tests; on the contrary, there was a sharp decline: from over 8,000 PCR tests a day to under 5,000 PCR tests per day.
PCR Tests are considered to be much more reliable than antigen tests. Antigen Tests are reported to give as high as 50%-60% false negatives (i.e. the Antigen Test result says a person is not infected by the coronavirus when in fact the person is infected - and infectious).
Consequently, it is worrying to see the Antigen Test replacing the far more reliable PCR Test in Delhi.
Consequently, since PCR tests in Delhi are being replaced by Antigen Tests, the combined results of all tests will show a false picture of a sharp decline in the positivity rate in Delhi. The primary reason for the overall decline is due to the increase in Antigen Testing.
4, CONCLUSION: THE CORONAVIRUS IS STILL RAGING IN DELHI WITH A HIGH POSITIVITY RATE - THE FIGHT IS STILL ON.
a) The positivity rate in Delhi has not fallen to the 5-6% as claimed by official figures. In fact, it is closer to 11-12% i.e. double the official figures.
b) Delhi's positivity rate of 11% is still dangerously high - and is about the same as the all-India average positivity rate of 11-12%.
c) However, there is a marked improvement in the capital's positivity rate from 34% just a month ago - to 11% today (focusing on the exclusive results of only PCR Tests, the only reliable testing method).
d) It is crucially important not to relax into self-congratulatory mode - and ensure there is no let-up in the fight against the coronavirus: to ensure that this improving trend continues.
POLICY IMPLICATIONS: SHOULD INDIA USE ANTIGEN TESTS AT ALL?
1. The Government must recognise that Rapid Antigen Tests are unreliable - and worse, they are misleading. Do not announce positivity rates based on RAT results - these are false.
2. However, it is worthwhile continuing to use Antigen tests but only on three conditions:
i) Do NOT bother with RAT's negative results. Treat all RAT negative results as meaningless and to be thrown into the nearest bin
ii) However, do take the RAT positive test results seriously and quarantine/self-isolate all those who test positive.
iii) Do NOT incorporate RAT positivity test rates in the overall data for policy purposes this will lead to false optimism and mislead both the public and the policy makers.
3. Do NOT reduce the number of PCR tests (as is currently happening) - in fact Increase the number of PCR tests rapidly.
4. Be very selective and careful in which particular make of RAT kits are being used. There are numerous low quality RAT kits on sale by dubious organisations profiting in this pandemic.
5. Ideally use only RAT tests that have been FDA or EU approved (or cleared after rigorous kit testing by the ICMR).