Get the testing strategy right to control Covid-19

By: |
September 8, 2020 5:45 AM

After some prodding by the Delhi High Court which wanted the capital to change its testing strategy following a surge in infections once again, ICMR has finally given states the freedom to come up with their own testing protocol.

Till now, one of the reasons for the ‘case infection rate’ being much lower than the serosurvey was the various restrictions put on testing. (Reuters file image)

Several parts of the country may or may not be witnessing a second wave of the novel coronavirus as AIIMS chief Randeep Guleria has indicated could be happening, but what is very evident is that the testing strategy being used is quite inadequate. That is why, in cities like Delhi for instance, while the daily tests show a ‘case infection rate’ of just 10.8%, the serosurvey suggested that 29.1% of the population had Covid-19 at some point, up from 23.5% in the serosurvey conducted in July. And, in the case of Mumbai, while the ‘case infection rate’ is 18.9%, the serosurvey suggested that 33% of the city had been infected by Covid-19. Since the serosurvey is based on a rigorous sampling technique, it is more likely to be representative of the situation on the ground.

Till now, one of the reasons for the ‘case infection rate’ being much lower than the serosurvey was the various restrictions put on testing. So, for instance, walk-in testing was not allowed, testing was initially to be done only for those who came in from abroad or those who were in touch with infected persons, etc. Over time, the restrictions were loosened. People can, now, walk in and get a Rapid Antigen Test (RAT) and many offices are, in any case, also doing their own antibody tests; an RT-PCR test, however, is still not a walk-in-sans-prescription till now.

As this newspaper has been arguing for some time, one of the reasons why there has been a big dip in India’s ‘case infection rate’ is because the ramp-up in testing has mainly been via the RAT test—75% tests in Delhi and 90% in Bihar are RAT today—which, as the Delhi government affidavit to the Delhi High Court said is able to detect Covid-19 at a third the level of the RT-PCR. This poor level of detection, coupled with a very low level of testing, is an important reason for the faster spread of Covid-19. When initial infections are not detected, this allows infected persons—either symptomatic or asymptomatic—to continue to infect others.

Indeed, as FE showed with data on Monday, any country or state/city that tests a high enough number of persons initially has a better chance of being able to contain the infection than others. The US, by way of example, did 57 tests per thousand persons on June 1 as compared to India’s 2.9. So, between June 1 and September 5, when testing picked up in India, its infections grew much faster than those of the US; while India’s infections rose 21.1 times, those of the US rose just 3.5 times. The same results can also be seen within India. Since Mumbai and Delhi have tested a lot more than other cities and states, when they ramped up their testing between June 1 and September 5—along with other cities/states—this resulted in a far slower growth in new infections.

After some prodding by the Delhi High Court which wanted the capital to change its testing strategy following a surge in infections once again, ICMR has finally given states the freedom to come up with their own testing protocol. Now that this has happened, states should ensure that walk-in tests without doctor’s prescriptions are allowed for RT-PCR tests as well. And if they are using a lot of RAT because of their lower costs and faster turnaround time, they should follow the protocol and retest all those who turn out to be negative with an RT-PCR test as that is more reliable. Such a strategy will be the perfect combination of speed, economy and accuracy. The right testing strategy, keep in mind, is critical if Covid-19 has to be kept under control.

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