At the core of Delhi’s transition from corona capital to a model city where the number of COVID-19 cases has been consistently falling is possibly its testing strategy, say experts as they try to decipher the trajectory of the disease.
Though there are no precise answers to the many questions of whether the Delhi curve has plateaued, dipped decisively or reached its peak, a close examination of testing patterns could hold the key.
While some scientists believe ramped up testing has helped in breaking the transmission chain, there are others who say the reduced numbers could be because of the focus on the rapid antigen test that can throw up false negatives.
Testing helps in identifying and isolating the infected, thus breaking the transmission chain, said Anurag Agarwal, director of the Institute of Genomics and Integrative Biology (IGIB).
Ever since the antigen tests came, many more have been tested than previously. It breaks the chain, then they go into isolation. The number of people that each infected person infects goes down if you find them early, Agarwal told PTI.
In virologist Shahid Jameel’s view, rapid antigen tests don’t have the same accuracy as RT-PCR tests. He, however, noted that the number of patients at hospitals has also been going down in the last three-four weeks. “Delhi has almost completely switched to antigen based tests. A very large amount of tests are antigen tests and they have sensitivity of 50-60 per cent. It is possible that the reduced numbers that are because of the low sensitivity of the antigen test,” said Jameel, CEO of the Welcome Trust/ DBT India Alliance.
Referring to lab sensitivity, he said the nasal swab, for instance, has to be put deep into the nasal cavity and maybe not everyone is trained adequately. “I am not saying that’s the only reason. But that may be skewing the data a bit. We may actually have the outbreak going down. One good evidence of hospitals is they are no longer as crowded as they used to be. But I would say don’t believe in absolute numbers but may be the trend is alright,” Jameel told PTI.
In terms of absolute numbers, June figures can tell a story.
On June 23, Delhi recorded 3,947 fresh cases, the highest daily number of cases in 24 hours since the outbreak. On Wednesday, one month later, the number was 1,349. This is part of a two-week pattern with the city witnessing a steady decline in the number of fresh cases since the last two weeks.
Delhi has 1,25,096 cases with 3,690 fatalities, according to Union Health ministry figures on Wednesday. Of the total number of cases, 15,288 are active and 1,06,118 are cured/discharged. The numbers have improved steadily since June. The recovery rate which had fallen to nearly 36 per cent last month has now risen to 84 per cent, much higher than the national recovery rate of 62.72 per cent.
On June 11, the Delhi High Court observed that the city was headed towards becoming the corona capital of the country. It was also the first city in the country to report one lakh cases. The turning point could well have been when the Ministry of Home Affairs stepped in to announce rapid antigen tests for the city. The number of tests went up from about 7,000 a day to more than 20,000, almost three times that number.
According to Giridhar R Babu, epidemiologist and professor at the Public Health Foundation of India (PHFI), transmission can be contained only when the cases are detected as early as possible and isolated.
“Delhi has increased testing and that has gone in the favour of identification of cases as early as possible and then isolation,” Babu told PTI. Babu said there can be no lowering the cases without reaching the peak. “To reach the peak, we have to ensure that mortality is reduced. To do that, we have to employ testing widely. Once you increase testing, you have to mount up your hospital system and all these things go hand in hand,” Babu said.
Could Delhi have reached the peak? Agarwal pointed to the serological survey released on Tuesday to make his point.
The survey, conducted across 11 districts with a sample of 21,387, said 23.48 per cent of Delhi’s people are affected in Delhi. That is, almost one in five people in a city of about 20 million.
Generally, when serology positivity hits 20 per cent is when the first peak happens pretty much all over the globe, he said. Delhi and Mumbai seem to have got to the point. Delhi peaked at the end of June. This is not herd immunity and there may still be a second peak or a slowing of the decline when we reopen further, he cautioned.
His institute, the IGIB, which falls under the Council for Scientific and Industrial Research, has also been involved in genome-sequencing of the coronavirus. “One of the main reasons behind the number going down is that a large number of people have been affected and recovered, mostly by asymptomatic or minimally symptomatic undiagnosed infection,” Agarwal said.
There is little possibility of re-infection in the short term so this number, probably around 20 per cent, prevents further rapid spreading because the high-interaction high-risk spreaders are a big part of those already infected and recovered, he said.
On Monday, AIIMS director Randeep Guleria also said Delhi seems to have hit the COVID-19 peak but cautioned against lowering the guard. After the MHA intervention, the Delhi government changed its containment strategy.
On June 26, it was decided to re-map containment zones to divide them into micro clusters for better surveillance and contact-tracing. There were 280 containment zones on June 26. On July 20, the number was 696.
The total approach of dealing with the pandemic has changed, said B L Sherwal, medical director of the Rajiv Gandhi Super Speciality Hospital, a dedicated COVID-19 facility. Earlier, there were some lacunae and that gap analysis was done. The treatment also has improved. Now the area has been earmarked and very small containment zones have been carved out.
He added that there is a decline in the number of patients being admitted, in the death rate and also in the number of critical care patients. Mahesh Verma, head of the Delhi government panel to strengthen the preparedness of hospitals to battle the coronavirus, was also cautious.
“We need to wait for some more time to say it is truly declining. It has been almost two weeks since the cases have declined. Fewer patients are coming in and only those are coming in who require critical care,” Verma said.
The other factor at play has been home isolation.
“Because of this home isolation model, testing in Delhi has increased. Earlier, people were scared of getting tested because they thought they would be put into quarantine centres if they are tested positive for corona,” Chief Minister Arvind Kejriwal said last week. Home isolation worked in Delhi’s favour, agreed Sandeep Budhiraja, group medical director of Max Healthcare. “If there would have been no consensus on home isolation, there would have been a burden on healthcare facilities and people would have not come out for testing for fear of institutional quarantine,” he said.