Faulty test strategy swings positivity rate

TPR of Sundargarh, which has 2nd highest active cases after Khurda, fell from 52.3 pc on May 7 to 19.7 pc on May 8
Representational Image. (Photo | PTI)
Representational Image. (Photo | PTI)

BHUBANESWAR: From a test positivity rate (TPR) of as high as 70.1 per cent (pc) on May 8 to suddenly 34.5 pc next day, Bargarh, one of the worst Covid-19 hit western Odisha districts, seems to have seen the highest drop in positivity rate in a day.

The TPR of Sundargarh, which has the second highest active cases (10,039) after Khurda (12,742), fell from 52.3 pc on May 7 to 19.7 pc on May 8. Similar was the case with Kalahandi and Nabarangpur where the positivity rate came down from 55 pc and 58.1 pc on May 1 to 34.5 pc on May 5 and 29.8 pc on May 2 respectively.

But is it possible? What is the strategy behind it? Not only the western region of the State but also some of the coastal districts have been witnessing such wild swings in positivity rate, which is a vital indicator in assessing the spread of an outbreak.The percentage of people found to be infected with the virus in Ganjam district was 81.6 pc on May 1 and it dropped down to 6.3 pc next day.

Blame it on the testing strategy. Even as the State has been reeling under a fierce second wave of the pandemic that has been infecting and killing more, the government is yet to ramp up testing and increase RT-PCR share. As mandated 70 pc RT-PCR tests of the whole tests, it has been hovering around 40 pc. An analysis of the date-wise sample collection data and detection of cases revealed, when the share of RT-PCR tests is more, the TPR is high. If one district is found to have more TPR one day, it will have more antigen tests the next day to cover up the positivity rate.

Apart from share of RT-PCR tests, the TPR also depends on the number of tests when the infection is spread across the length and breadth. The positivity rate is bound to fluctuate if there is a drastic shift in number of tests and difference in share of RT-PCR and rapid antigen tests (RATs).

Sample it. The day Bargarh recorded over 70 pc TPR the share of RT-PCR test was 270 out of total 610 tests. On the next day, the share of antigen tests was 992 out of 1,383. When the TPR in Ganjam was 81.6 pc, the district had conducted 179 RT-PCR tests and 28 RATs of the total 207 tests. The next day the share of RAT was 3,559 out of 4,161 tests.

“We have been doing testing as per the target given. We have been asked to conduct 1,100 tests a day including 20 pc RT-PCR. The number of tests some time is less due to shortage of RAT kits,” said a district official from Bargarh.The analysis also found maximum RATs in districts where the infection is low though the ICMR has been insisting to conduct as many RATs in the containment zones in the districts that have been reporting a high number of cases. 

According to health experts, it should not be the strategy the way the Odisha government is handling the testing. When the overall TPR is around 25 pc, the number of testing should not be less than 80,000 with at least 60 pc RT-PCR. Microbiologist and former member of ICMR Dr Tribhuban Mohan Mohapatra said it is difficult to know the actual infection rate when the testing protocol is not properly adhered to. 

“The TPR has no meaning if the share of RAT and RT-PCR is not properly distributed. Almost all districts are in the grip of the virus. People are hiding symptoms and getting treatment at home without the knowledge of the administration. The only strategy should be to test more and isolate as many people,” he said.

Health authorities, however, claimed that the testing strategy is based on the ICMR guideline. Director of Health Services Dr Bijay Mohapatra said the focus is now to conduct more RT-PCR tests in the districts that are having high TPR.  “The fluctuation in positivity rate may be due to occasional delay in RT-PCR testing,” he reasoned.
 

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