Covid-19: What you need to know today

India needs a new testing protocol. Actually, any country that is continuing to see a rise in coronavirus disease (Covid-19) infections needs one. Bill Gates, the founder of Microsoft, and one of the clearest thinkers when it comes to issues related to health, recognises this. In recent interviews, he has been harshly critical of the testing process in the US, going so far as to term it worthless. Gates’s issues are with access and delays. Some people in the US are waiting a week up to 10 days for their results. That doesn’t help. Not everyone who gets tested is in quarantine or self-isolation, which means an early result can sequester them and prevent them from infecting more people (that’s how the chain of infection is broken).

The problem is that the best tests for Covid-19, the molecular ones such as the Reverse Transcription Polymerase Chain Reaction (RT-PCR) test, take at least 48 hours to show results. Add delays caused by logistics and backlogs, and the average time in which results for such tests come out is between three and four days. That’s the number cited by public health officials across most states in India (and at least in states where complete or partial lockdowns are still on, there is some amount of enforced quarantining and social distancing), although there have been reports of delays from some states. The fact is, India has increased its testing game and can conduct at least 500,000 RT-PCR tests a day now, up from a few thousands.

But more are needed, and, sometimes, time is of the essence – which brings us to rapid antigen tests, which now account for around a fourth (and on some days a bit more) of tests being conducted in India.

This column has previously focused on antigen tests, and when they are best used. Simply put (and there is no change in this writer’s position), antigen tests are best used when time, not capacity, is a constraint. The only way to deal with a capacity constraint is to acquire more capacity. So, if Covid-19 cases in a hot spot or containment zone are peaking, and there is an urgent need to test a large number of people in a short period of time, and isolate or treat the infected so as to prevent further infections, an antigen test may be the best fit. Or, if, as in the US, tests are taking a week to 10 days, then an antigen test may serve the purpose. The results of these tests are usually available onsite, and within the hour. This could explain why there is a sudden clamour for antigen tests in the US (and it is clear that its use wouldn’t be out of place in some states or some counties where cases are soaring; parts of California, for instance, seem ideal candidates for such tests). That applies to India too – antigen tests would definitely help in parts of the hinterland and the peninsula that are seeing a surge in cases.

But (and it’s a big one), there is a problem with antigen tests, one that, again, has been mentioned in earlier instalments of this column – the high false negative rate. This means that an infected person is identified as uninfected. According to multiple research studies, the proportion of false negatives ranges between 20% and 50%. Which means that at least one in five people, and as many as one in two, is erroneously identified as uninfected despite carrying the virus. The main reason (it isn’t the only one) for this error would appear to be the inability of antigen tests to amplify the viral protein (in contrast, RT-PCR ones have the ability to identify even traces of the virus on the basis of their genetic material, which is what makes them accurate). So, what’s the solution?

Interestingly, one part of the solution is already part of the guidelines issued by the Indian Council of Medical Research, or ICMR, as part of its antigen testing protocol – that those with symptoms of Covid-19 or SARI (severe acute respiratory infections) who are shown to be negative in an antigen test, be administered the RT-PCR test.

Another would be to take multiple samples (two should suffice) from anyone appearing for an antigen test, and testing them, ideally using two different antigen tests (each one is different), or, if unavoidable, even the same one but separately. If there is a discrepancy between the two test results, then the person should be asked to undergo the RT-PCR test.

With more Indian states using antigen tests (in addition to RT-PCR ones, and not always when they should be using them), ICMR should issue a new testing protocol that mandates: when antigen tests can be used; how antigen tests should be conducted (two simultaneous ones as described above); and the follow-up.