Rising cases, positivity indicates need to expand, randomise testing
With Delhi registering more than 1,000 cases of coronavirus disease (Covid-19) for the second day in a row on Friday, the proportion of tests returning a positive result continued to rise even with the number of tests going up, prompting experts to call for a more aggressive and randomised testing strategy.
With an average of 5,624 daily tests performed in the last seven days, the average daily positivity – or the percentage of people who test positive in the last week – was 12.6% for the week ending May 29. Last Friday, the average daily positivity rate for the seven days before it was 9.9% and the corresponding number was 6.4% for the week before. In the last 30 days, this average has nearly doubled from 6.5% on May 1 to 12.6% on May 29.
Delhi’s positivity rate also remains much higher than the national average of 6.1% till Thursday, the latest this data was made available according to the Indian Council of Medical Research (ICMR).
In the same time, the average number of samples tested in a week has increased to 5,624 on Friday, from 5,009 a week ago, according to data released by the Delhi government. To be sure, Delhi’s testing numbers have been the highest among the worst-hit regions in the country and the Capital has performed 10,075 tests for every million residents, nearly 3.5 times the national average.
Experts pointed out that the positivity rate can be heavily influenced by a targeted testing strategy.
“The positivity rate depends on the testing criteria. Who are you testing? If you are only testing those who are likely to have the infection such as someone from a containment zone with fever, then the positivity rate will be high. Having said that, the positivity rate is increasing along with the absolute number of cases as well, which shows that transmission is happening. And, India is on the upwards trend; the numbers are likely to go up further with travel being resumed,” said Dr GC Khilnani, chairman of PSRI Institute of Pulmonary and Critical Care and former head of the department of pulmonology at AIIMS.
Dr Shobha Broor, former head of the department of microbiology at AIIMS, suggested that randomised antibody tests be conducted in the community to understand the underlying burden of the infection and the number of people who were asymptomatic carriers. “Sero-surveillance (population level monitoring of antibodies that remains in the blood even after the infection is cured) will help us in understanding the trend of the infection as well. And, it is likely that as more and more asymptomatic transmission happen, the virulence or the severity of the infection will reduce over a few months with it later becoming endemic,” she said.
Delhi, as per national guidelines, has been testing all those with influenza like illness or severe acute respiratory infection and asymptomatic high-risk contacts of a person who has tested positive for Covid-19.
In April-end, Delhi had started reporting huge pendency of samples, especially those collected from the containment zones hurting the city’s contact tracing measures. Delhi health minister Satyendar Jain had raised the issue on April 28 with the union health minister Dr Harsh Vardhan, as the pendency was the highest at the centre-run National Institute of Biologicals in Noida. A day after the meeting, the government stopped sending samples to the laboratory till the pendency reduced.
On May 4, the Delhi High Court directed the government to ensure that the samples are tested and reports provided within 48 hours.
“Yes, we need to test more people to contain the spread of the infection by identifying cases and isolating them early on. However, there is a capacity of the laboratories – they still have the same number of staff, the tests take a few hours to perform, all biosafety measures have to be taken. So, even though in an ideal situation we should test the asymptomatic people, but currently we do not have the capacity to perform so many tests,” said Dr Broor.