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Centre tells states: Do RT-PCR to catch false negatives after rapid antigen test

Symptomatic negative cases are those where the patient has symptoms of Covid, but tests negative. Since rapid antigen tests are known to have high degre of false negatives, the ICMR had mandated that symptomatic negative cases must get a retest through RT-PCR.

Written by Kaunain Sheriff M | New Delhi |
Updated: September 11, 2020 7:33:50 am

Reiterating that all symptomatic negative cases of rapid antigen tests (RAT) must mandatorily take an RT-PCR retest for Covid, the Centre on Thursday directed all states to set up two teams each, at the level of the district and the state, to monitor and ensure that no potentially positive case is missed out.

Symptomatic negative cases are those where the patient has symptoms of Covid, but tests negative. Since rapid antigen tests are known to have high degre of false negatives, the ICMR had mandated that symptomatic negative cases must get a retest through RT-PCR.

Explained| How the coronavirus (COVID-19) test works

Government sources, part of the team monitoring the pandemic, said the decision came after they found that a “few big states” are now reporting a significantly high percentage of symptomatic negatives not being retested through RT-PCR, thereby spreading the infection among the general population.

“When we did data analytics, which is done on daily and weekly, we found in a few states only 30-35 per cent of symptomatic negatives were undergoing RT-PCR test. Which means, roughly 70 per cent of symptomatic negatives were still spreading the infection,” source said.

Sources said while trends differ across states, nationally, of the total tests, 65 per cent are RT-PCR and the remaining RAT. However, sources underlined that there is no correlation between states conducting high number of RATs and those reporting a higher percentage of asymptomatic negatives not being retested through RT-PCR tests.

For instance, sources pointed out, Bihar, which is currently conducting 80 per cent RATs and 20 per cent RT-PCR tests, was not found to be reporting a higher percentage of symptomatic negatives not being retested through RT-PCR. “Proportion of rapid antigen to RT-PCR has nothing to do with retesting. Retesting is the question of the state’s efficiency or incompetence. Our focus is only to retest the symptomatic negatives,” sources said.

Also in Explained| How India tests for Covid-19 

To track this closely, states have been directed to set up a monitoring mechanism in every district. “Although this has happened in very few states, we have written to all the states saying they should have a designated individual at the district level or a district-level team which should be doing daily monitoring of the symptomatic negatives in the district. Similarly, they should have a team at the state level, which should collect this data and conduct a review on a daily basis. They should analyse what is the universe to be subjected to RT-PCR retest, and then they must be covered immediately so that their potential to spread the infection is curbed,” a source said.

In its advisory to states, the Centre has reiterated ICMR’s guidelines that two specific categories of persons must get a retest through RT-PCR: all symptomatic negative cases of RAT; and asymptomatic negative cases of RAT that develop symptoms within 2 to 3 days of being tested negative.

ICMR guidelines mandate compulsory retesting of symptomatic negatives in the backdrop of RAT’s sensitivity ranging from 50 per cent to 85 per cent, depending on the viral load of the patient. So, to rule out false negatives, where the patient may spread the infection, the ICMR has mandated that if any person develops symptoms days after he tests negative after RAT, that persons should get an RT-PCR test.

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