Experts puzzled by Karnataka's falling Covid-19 positivity rate amid 'complacency'

More and more people are exposing themselves to Covid-19 by moving about in the streets, but the state’s official test positivity rate (TPR) has plummeted by nearly seven points. This could be because many asymptomatics are slipping under the radar, an expert said.

The TPR is a way to measure containment. The smaller the percentage, the better. According to Covid-19 mobility data compiled by Google, the average movement of people statewide is about 25% below the pre-epidemic baseline. Despite being under the baseline, there have been substantial increases of people stepping out.

Over a six-week period from September 4, there was 6% increase in retail visits and recreation, a 9% increase in visits to supermarkets and pharmacies, a 6% in visits to parks, a 5% increase in the use of public transport and a haphazard 17% increase in workplaces opening up again.

Official data for the same period shows that the statewide TPR has dropped from an average of 14.7% six weeks ago to 7.78% this week, which puts the rate close to the 5% top baseline set by the World Health Organization (WHO) to indicate good clinical management. However, as DH had reported last week, the inclusion of retests means the actual TPR can be almost 2% higher.

‘Virus under control’

Nevertheless, the drop is a positive step for the state, experts said, as it matches the Covid-19 trend in other states. Health Minister Dr K Sudhakar suggested that the declining TPR is a result of increasing tests being carried out. “The virus is under control,” he said.

Nevertheless, the key could be asymptomatic patients, said Dr Manindra Agrawal of the IIT Kanpur, who is a member of the Covid-19 Supermodelling Committee.

He suggested that the TPR is low because a vast majority of asymptomatic Covid-19 patients never get detected by the surveillance machinery.

“Covid-19 is unique because it results in a large number of asymptomatic who are never detected. They never need any medical intervention and so they go unnoticed. At the same time, they do contribute to the spreading of the infection so it becomes difficult to estimate how many infections there are at present,” he said.

He added that continued TPR drop amid increased mobility may also be happening because people are continuing personal hygiene and social distancing
protections.

To at least one expert, the increase in tests and decreasing burden in areas which have seen a surge in cases or both has also helped. “The surge in cases is receding, at least in few areas with higher population density compared to others,” said the noted epidemiologist Dr Giridhar Babu.

However, another expert, Sanjeev Mysore, Convenor of Jeevan Raksha Covid-19 analysis project, said Karnataka’s TPR has never really dropped. By calculating the total number of cases and the total number of tests, the TPR is a solid 11.4%. “This number has never really changed,” he said.