Around 0.8% of over 7 lakh people in Delhi tested for Covid through the rapid antigen method have been retested through RT-PCR so far, of which 11% have come out as positive, according to data obtained through an RTI. Rapid Antigen Tests (RAT), which can produce results within 30 minutes, were introduced in Delhi on June 18 after a decision was taken by the Centre and Delhi government to scale up testing in the city, where the positivity rate had crossed 20%.
Between June 18 and August 27, the city saw approximately 7,45,892 rapid antigen tests. According to guidelines of the Indian Council of Medical Research (ICMR), a person testing negative through RAT method should “definitely” be retested through RT-PCR if he or she shows symptoms of Covid-19.
In response to an RTI query filed by The Indian Express, the National Health Mission nodal officer of south-west district said, “Total number of samples that were re-tested through RT-PCR method after having tested negative through RAT method in Delhi between June 18 and August 27 are 6,054.”
This would imply that out of over 7.45 lakh people to have taken the RAT over the span of three months, only 6,054 were showing symptoms such as flu, cough or fever. While a district-wise break up was not immediately available, the west district, it is learnt, has carried out 129 such retests so far.
The RTI response added that out of the 6,054 RAT samples re-tested through RT-PCR, 699, or 11.54%, came out as positive.
The findings assume significance in light of Delhi’s heavy reliance on RAT to isolate positive cases and curb the spread of the virus. The number of RT-PCR tests, which started much earlier in February, were 6,58,132 between June 18 and August 27.
ICMR says RAT should be carried out among all patients showing influenza-like infection symptoms in containment zones, asymptomatic direct and high-risk contacts with comorbidities in healthcare settings. It advised a “combination of various modes of tests” to scale up testing.
The Delhi government has over the months carried out mass scale rapid tests among high-risk groups such as street vendors, cab drivers, workers in industrial townships, domestic helps, etc.
“It is no surprise that RAT tests have surpassed RT-PCR tests because the very purpose of rapid tests is to expand testing quickly and cover vulnerable sections of the population. RT-PCR on the other hand could so far be availed only by those with prescriptions. Doctors at all rapid test centres were advised to ensure every symptomatic person testing negative undergo reconfirmatory RT-PCR. Otherwise undetected cases declared as negatives would infect others. Whether that instruction has been followed remains to be seen,” a chief district medical officer said.
According to ICMR, rapid tests have a sensitivity of 50.6% to 84%, which makes retesting symptomatic individuals essential.
Between June and July, the city conducted 2 lakh RT-PCR and 3 lakh rapid tests. While RT-PCR had a positivity rate of 30.5%, it was 6.5% in RAT. Till September 9, Delhi carried out 19,03,780 tests — RT-PCR and RAT combined, which translates to 1,00,198 tests per million population.
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