Smell a RAT: The COVID-19 curve may not be flattening

On Monday, India reported its lowest tally of daily infections in the last 20 days, adding 75,083 cases and recording 1,01,468 recoveries. In fact, over the last four days, India has reported more recoveries than infections. Usually, a higher recovery and a lower positivity should be a sign of the curve flattening but in India’s case, this may not be true.

An analysis of daily testing and infection data across states show the recent drop in infections, and, hence, positivity rate may be largely due to some states pulling back on testing and others using more of the less reliable rapid antigen test (RAT) kits. On Monday, for instance, Delhi nearly halved testing levels from 62,669 a week ago to 33,733 while Bihar conducted 1.73 lakh tests, most of them using RAT kits.

Moreover, over the last two days, nearly a fourth of India’s tests were conducted by Bihar whose share of total testing has been steadily increasing. While on August 1 Bihar conducted only 4.3% of India’s tests, as the state ramped up testing using RATs, the share increased to 8.9% on September 1. By September 21 the share had jumped to 24.1%.

Meanwhile, Bihar’s positivity ratio has been falling. While India’s positivity ratio was 8% on Friday — a smaller number of 9,33,185 tests were conducted and 75,083 infections recorded – Bihar’s positivity had dropped to 0.4%. In contrast, Tamil Nadu, which conducts only RT-PCR, had a positivity of 6.6%.

Uttar Pradesh is another state where positivity has remained low; despite 1.4 lakh tests, positivity was only 3.4% on September 22. In Gujarat too, despite sero-surveys indicating higher infections, positivity has dipped after the state started doing more RATs. Gujarat’s positivity has fallen from 10.5% on July 22 to 2.3% on September 22.

Neighbouring Maharashtra, on the other hand, recorded a positivity of a whopping 39.3% on Friday. In Karnataka, though, it was a more moderate 17.2%.