New Delhi: India’s Covid-19 burden is touching new highs every day, but the national positivity rate has continued to hover around the 7-8 per cent mark, except on Sundays, when the testing numbers fall and the percentage of positive cases crosses 9 per cent.
Experts say this could mean the incidence of infection across the country has remained largely constant, though there are wide variations in positivity rates between states — Delhi sits atop the list with 23 per cent positivity rate, low-testing Telangana has registered 18 per cent, while West Bengal has just 3.5 per cent.
Testing numbers have more than doubled between 1 and 23 June — from 1,00,180 to 2,15,195. Senior officials involved in the Covid-19 strategy say the eventual target is to do 5 lakh tests every day.
The most interesting data emerged out of 20 June — 1,90,730 tests were conducted across India, the second highest number for a single day so far, and the positivity rate was recorded at 12.33 per cent, the highest so far. This could indicate a need to further expand the testing base.
Revision of strategy
India’s testing strategy was revised Tuesday, when the parameters for antibody tests were widened to include ‘high risk’ professionals such as the police, drivers, shopkeepers, migrants, healthcare workers as well as vulnerable groups with compromised immunity.
However, the testing figures that ICMR updates every day include data only from the RT-PCR, TrueNat and CBNAAT tests — with the latter two being tuberculosis tests roped in for Covid testing last month.
Neither antibody tests, which are for surveillance purposes, nor the newly introduced antigen tests are included in the ICMR’s data.
Is India testing enough?
Dr Giridhara R. Babu, head of lifecourse epidemiology at the Indian Institute of Public Health, Bengaluru, said: “(If you look at) 23 June as compared to 1 June, the testing has almost doubled, but the positivity is 7.4 and 8.1 respectively… I don’t think we can say that it is range-bound given the varying capacity of the testing in different regions.”
However, he added, this value indicates that “even when we are increasing the testing numbers, the value of positivity relatively remains nearly the same”.
On the high positivity rate found on 20 June, Dr Babu said: “This might suggest that by doing fewer tests, we will not get the true picture. So, as far as I understand, we cannot say that there is a clear pattern here.”
He added, “Test positivity is a function of background prevalence of the infection and systematic approach of finding cases. We need to take these factors into consideration for analysis at the state level.”
Dr Anand Krishnan, professor at the Centre for Community Medicine at AIIMS, New Delhi, agreed that the positivity rate may indicate the infection rate is largely constant, but to decide whether testing truly reflects the disease burden, one needs to look at the testing strategy and how narrow or wide the “case” definition is.
Asked if India is testing enough, Krishnan said: “An expanded testing strategy would lead to lower positivity. We have been increasing the tests, but the problem is that we do not know how much testing would be enough for Covid.”
He explained: “For malaria for example, you take a sample of 1 per cent or 2 per cent of the population because you are aware of the population-level incidence. In this case, that is not known. Unless we have that data, we will never know whether we are testing enough.”