Fewer RT-PCR tests may catch Delhi off guard again


: The number of RT-PCR tests for Covid-19 has dropped in Delhi after a peak last week, data from the last four days show, prompting worries that any slackening in coronavirus testing efforts could catch the Capital off guard, like it has appeared to twice in the past, should the outbreak begin resurging.

At present, case trajectories show Delhi has successfully left behind its third, and the most intense, wave of infections that peaked in mid-November. The spike in cases at the time put the city’s resources to the brink, following which federal and state administrations intensified testing as well as hospital bed strength.

It resulted in the number of daily RT-PCR tests – the gold standard for coronavirus diagnosis – doubling from around 20,000 in mid-November to 40,000 recorded on December 4. The number, however, was 35,352 on December 5, before falling to 32,032 on December 6. In the December 7 bulletin, the number – which corresponded to a Sunday the day before – stood at 21,362 (it was 26,645 the previous Sunday).

Since November 15, the positivity rate has fallen from a peak of 13.6% to under 5% since December 4.

“It is very encouraging to see that the positivity rate in Delhi has remained below 5% for almost a week, especially since the government has increased the number of more accurate RT-PCR tests. However, this does not mean that the government can scale down the number of tests,” said Dr Lalit Kant, former head of the department of epidemiology and infectious diseases at the Indian Council of Medical Research.

Kant said maintaining RT-PCR numbers at the increased level was crucial. “If the current number of tests is maintained and the positivity rate continues to remain low, it will instil confidence in people that the number of infections have gone down and to keep an eye out for future increase in the number of cases,” he added, warning against any slackening on this front.

According to analysis of testing and daily case data, Delhi overcame its first two peaks after ramping up tests. However, in both cases, the increase in testing hit a plateau (particularly RT-PCR), which was followed by the beginning of the second and third peaks, highlighting the need for widespread surveillance to be kept up.

In the past, the Capital has relied heavily on rapid antigen tests, which have a lower sensitivity. These can fail to catch as much as 50% of cases, masking the true positivity rate and leaving many infected people undetected and at the risk of spreading the virus to others.

According to officials, Delhi is likely to see fewer RT-PCR tests on Tuesday. The problem causing the drop, they said, was due to the blockades at Delhi’s borders since many samples are sent to central government labs across the border.

“There are two labs in Noida where we send many of our RT-PCR samples. However, with the Bharat Bandh tomorrow, it is unlikely that we will be able to send the samples across. We have made provisions for storing the samples in our cold chain for tomorrow. These will be sent to the lab the next morning,” said a health department official, on condition of anonymity.

The farmer’s protest has also impacted sample collection as well. “Delhi government had set up many sample collection centres at the borders and ISBT where the collection has stopped at the moment,” the official said.

Overall, Delhi was able to scale up the number of RT PCR tests from an average of 14,300 tests a day during the first week of November to 32,700 on average very day during the last seven days. The RT-PCR tests accounted for 28% of the total tests that were being performed during the first week of November (seven-day average) in comparison to 45.2% of the tests conducted during the first week of December. The daily test share peaked at 52% on November 30, and was 40.15% according to the December 7 bulletin.

The rise was mainly due to substantial increase in the capacity for Delhi samples at central government labs, newer machines in many Delhi hospitals, and the mobile testing vans deployed by the centre.

“The central government has given us extra capacity in their labs in Noida, Ghaziabad, and Gurugram. In addition, there were some private labs in the neighbouring areas which were not utilising their complete capacity and the Delhi government is now taking their help,” said a second official from Delhi’s health department.

The existing labs have also been asked to work longer hours, even 24×7, to utilise 100% capacity, said a third official.

Officials said they are also trying to ease bottlenecks in processing and reporting tests.



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