Fast rise in Rapid Antigen Tests percentage among total COVID tests
South 24 Parganas had conducted 92 per cent rapid antigen tests during the January 21-27 week. West Bengal’s sharp slide in COVID-19 positivity rate over the last fortnight, the quickest in the country, may be linked to high percentage of Rapid Antigen Tests being carried out during the fortnight; a section of public health experts in the state have said.
West Bengal’s COVID-19 positivity rate has plummeted nearly five times between January 10 and January 25, during which the RAT number has almost trebled, with a sharp slide in the positivity rate.
The state’s positivity rate was five per cent February 1. It can now go down to one-two per cent in a week, according to media reports.
Experts have, however, expressed apprehensions that many affected persons may be missing the monitoring net.
The positivity rate has gone down. But the number of deaths continues to be a concern as more than 240 COVID-affected persons have died during the same period; fifth-highest in the country.
RAT increased, RT-PCR decreased
Some 14,500 RAT were carried out in state January 10, compared to about 45,450 January 25, according to state government data. Meanwhile, the RT-PCR number reduced by close to 20,000 comparing figures from the two days.
Read: COVID-19: Kerala’s alarming positivity rate challenges earlier claims of effective containment
This reporter accessed data from the Union Ministry of Health and Family Welfare. The data shows that West Bengal currently has the lowest RT-PCR test proportion within the overall COVID-19 test mix, considering the top eight affected states in the country.
West Bengal’s proportion of RT-PCR stands at 46 per cent based on the seven-day average till January 27. The same is 60 per cent for Maharastra, 64 per cent for Kerala, 79 per cent for Delhi, 61 per cent for Uttar Pradesh and even higher for south Indian states like Karnataka, Tamil Nadu and Andhra Pradesh.
Public health experts acknowledged the importance of RAT in quickly testing people while a pandemic was on the rampage.
But they also pointed out that RAT should not be taken as a conclusive test for being ‘negative’ and any symptomatic person found negative in RAT, should follow up with RT-PCR.
“RT-PCR is the gold standard for confirming positivity as it is much more sensitive than RAT and any symptomatic person, found negative in RAT, should repeat with RT-PCR,” Ajoy Sarkar, a frontline physician of COVID-19 and public health expert from Kolkata, said.
“RAT is important from a public health perspective. But here, the problem is that people have taken it as a definitive test. Hence, many people may be actually evading the monitoring net and continuing to spread the infection,” another expert from Kolkata, said.
The expert, attached to the state health department, reminded that it was quite common to find a person who had tested negative with RAT, tested positive with RT-PCR.
“Reducing RT-PCR and rapidly increasing RAT, just to make the COVID-19 rate going down rapidly may backfire as many affected patients will continue to evade the testing net and spread infection,” the official said.
A scientist at INSACOG (Indian SARS-CoV-2 Consortium on Genomics or Indian SARS-CoV-2 Genetics Consortium), national forum to monitor genome sequencing and virus variation within COVID-19 strains in India, observed that “while RAT is important, one has to ensure that a balance is maintained”.
The scientist warned that West Bengal should be careful not go the Kerala way, where high proportion of rapid tests at one point of time was considered one of the reasons for community transmission refusing to abate.
“Symptomatic individuals who have tested negative with RAT, should be linked with RT-CR test facilities. They should be urged to follow home isolation and treatment,” a communication by the Indian Council for Medical research, dated May 4, 2020, had said.
Why South 24 Parganas?
South 24 Parganas had 92 per cent RAT during the Jan 21-27 week, the highest in proportionate mix, according to Union health ministry data dated January 27. It had the lowest COVID-19 positivity rate in the state — 1.48 per cent — during the period.
In contrast, Kolkata had hardly eight per cent RAT during the period and recorded a 22.17 per cent positivity rate.
Similarly all other districts with high positivity rates — Kalimpong (36.9 per cent), Maldah (26.48 per cent), Birbhum (23.22 per cent) — had a higher RT-PCR proportion, of 60-76 per cent.
The finding has cast a shadow on the so-called ‘Diamond Harbour model’ of COVID-19 control that was put forward by Trinamul Congress (TMC) leader and Diamond Harbour member of Parliament (MP), Abhishek Banerjee.
The model has sparked off an acrimonious political debate within the ruling TMC as senior TMC leader and MP Kalyan Banerjee opposed Abhishek’s unilateral move.
Abhishek Banerjee rooted for strict implementation of COVID-19 norms within his constituency and initiated steps like arranging doctors on the wheel, stopping all political and other rallies and other social congregations and more importantly organised huge COVID-19 testing, particularly RAT, within his constituency.
On January 12, Banerjee organised 53,000 COVID-19 testing in Diamond Harbour, including at least 30,000 RAT according to his own admission that, many feel, has triggered to the RAT switch in the state.
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