Getting testing strategy right: India’s journey from March to July

From 2,500 tests a day at the lockdown’s start to 2.67 lakh tests yesterday, India has come a long way and it has a still longer way to go. One out of every 10 tests is returning positive with some states like Telangana recording much higher positivity rates than the national average. In recent weeks, there has also been a shift towards rapid antigen testing away from the time-consuming but rigorous  RT-PCR tests.

However, there are concerns about the sensitivity and specificity of the antigen tests, which could be the reason that ICMR has approved just one out of 14 kits that it received for validation. Test kits returning false negatives do not help India’s cause. It puts patients under a false sense of security and could intensify the viral spread and mortality rate. Additionally, it helps governments anxious to convey a return to normalcy a fig leaf to hang on to. In the first week of antigen testing,

The trouble with the rapid antigen test kit is two fold: one, it has to be stored at temperatures between 2 degree and 30 degree Celsius, while daytime temperatures during India’s hot summer rarely plummet below 30 C. Secondly, while the kit can detect true negatives(those who don’t have the virus) with a 99-100% specificity, the tests’s sensitivity (ability to detect true positive cases) ranged between 50.6 to 84% according to ICMR’s own reckoning.

Patients with higher viral load, showed higher sensitivity to the test during the validation process. Per se, this isn’t bad because studies saw patients with higher viral load are greater transmitters and are under greater risk of mortality.  ICMR has also mandated RT-PCR testing among symptomatic individuals testing negative to rule out false negatives. The big question is that whether this directive is being followed in cities like Delhi which have adopted antigen testing in a big way. The human tendency in such moments of crisis would be to move on from one patient to the next at the first sight of good news.

The advances made in recent months are no doubt phenomenal. From a shortage of RT-PCR kits, 68 firms have got approval for commercial use. Today’s Indian Express story points to a coming glut where domestic firms are complaining about zero import duty and export ban hitting their prospects and helping South Korean firms: a country that has banned RT-PCR kit imports. Five firms have also secured approval for IgG ELISA/CLIA tests for antibody detection and even small labs across India are putting ads inviting people to get tested for antibodies or join serosurveys for Rs.750. Also recall here the setback in April caused by flawed rapid antibody kits sourced from China.

Going by past record, there is also no reason why the antigen test kits won’t make good progress too in coming days. After Mumbai took the lead in doing away with doctor’s prescription for Covid tests and allowing walk-in testing, Delhi is also going the same way. Many cities are already going to hotspots or testing highly vulnerable persons like street vendors. Many hospitals are ordering antigen kits and TrueNat machines (a truely Indian innovation) for testing visiting non-Covid patients. In two months, barring an unmanageable spurt in cases, it is entirely conceivable that testing can be decentralised to the point that ICMR has difficulty recording testing outcomes and monitoring test kit supply.

Conversely, a massive scale-up of testing can prevent that unmanageable spurt in cases. States that went slow on testing in the belief that fewer tests equates to fewer Covid cases to deal with only to find the virus showing its presence through spiking positivity rates even in the fewer tests done have hopefully learned their lesson. Credit for the rising recovery rates–over 60% today–lie with increased testing. We owe higher testing to our embattled health workers who have known no rest or peace of mind since early-March.