The way to test the entire country is to do the kind of antibody tests or sero-surveys that ICMR did last month regularly to see which parts of the country are more likely to have a higher disease burden.
While home minister Amit Shah promised a quick ramping up of Covid-19 testing in Delhi, from the current 8,600 per day to 18,000 by June 20 and, finally, testing-for-all, it is not clear how this can be done till the Indian Council of Medical Research (ICMR) changes its guidelines on testing. The guidelines essentially restrict testing to symptomatic persons, save for exceptional circumstances like a direct contact and high-risk contact of someone with Covid-19. It is these guidelines that Delhi chief minister Arvind Kejriwal further tightened (later rescinded by lieutenant-governor Anil Baijal).
One way to reach the stated goal is by using the new antigen test that has just been approved by ICMR. Unlike the RT-PCR that is the gold standard but takes upto 24 hours for the result to be generated and needs to be carried out in a laboratory, the rapid antigen detection test is a point-of-care test, that is, the test can be conducted at the site where the subject is, without needing a laboratory setting, and the result generated in just 30 minutes.
The test involves detection of the viral antigen (surface proteins, like the spike protein, that SARS CoV-2 has) by the kit, and is to be conducted under medical supervision. But, in this case too, ICMR has put needless restrictions; the test is to be used in containment zones and healthcare facilities only, that too in very specific cases.
Ideally, the restrictions should all go. The way to test the entire country is to do the kind of antibody tests or sero-surveys that ICMR did last month regularly to see which parts of the country are more likely to have a higher disease burden. While a sero-survey, or antibody test, may miss out those who have been exposed to the virus but haven’t developed antibodies yet, the rapid antigen tests has a true positive rate of 50.6-84%, depending on viral load. In an office or an apartment complex or residential colony, for instance, an antigen test can be administered quickly. But, the test gives a large number of false negatives; that is, a person with Covid-19 can be declared not-infected, though the flip side is that a person who doesn’t have Covid-19 will not be declared as having the infection (false positives, in jargon). So, if the antigen test is administered to 100 persons and 70 are declared to be infected, the remaining 30 can be tested using the RT-PCR to know for sure about the infection.
The government should also explore options like Israel’s breath-test for Covid 19—the Times of Israel reports the development of a spectroscopy-based breathalyser test that gives results in under a minute, using the physical properties of the virus such as size and electrical properties to detect changes in the resonance in the observed spectral frequency range once a subject breathes into the breathalyser. India nees to marshal all resources it can for ubiquitous testing, and the sooner this is done, the better.