Nearly one-quarter of Delhi infected with coronavirus, survey reveals

Experts are calling for urgent further study after a survey found almost a quarter of all people in Delhi have been infected with coronavirus.

The serological survey was carried out by the Delhi government and India’s National Centre for Disease Control (NCDC), and saw a sample of more than 21,000 people across the capital’s districts tested.

It found that 23.48 per cent of those surveyed had been infected, dropping to 22.86 per cent when adjusted for false positives and negatives, NCDC chief Dr Sujeet Kumar Singh told reporters at a press conference on Tuesday.

The survey did not diagnose current illnesses – rather, it analysed blood samples for the antibodies that fight off the Covid-19 virus, and which therefore serve as a marker of past infection.

The results indicate infection has spread among a far higher percentage of the population in Delhi than the city’s 125,096 confirmed coronavirus cases and 3,690 deaths would indicate.

Delhi has an estimated population of around 29 million people, meaning the survey points to around 6.5 million missed or asymptomatic cases.

Last month Delhi overtook Mumbai to become India’s worst-affected city, and while hospitals were never completely overwhelmed, there were a number of high-profile cases of severely ill patients being turned away by doctors. Cases reached a peak of 4,000 new infections a day in mid-June.

In a press release, the central government health ministry hailed it as positive news that “only 23.48 per cent” of Delhi’s population had been infected. It attributed this to “proactive efforts taken by the government to prevent the spread of infection, including prompt lockdown, effective containment and surveillance measures including contact tracing and tracking, as well as citizen’s compliance [to emergency regulations]”.

India as a whole went under the world’s earliest and strictest national coronavirus lockdowns, before it was eased in May to protect an economy in free-fall. Cases have since risen dramatically to more than 1.2 million, putting India third in the world for cases after the US and Brazil.

Dr Chandrakant Lahariya, a Delhi-based epidemiologist and public health specialist, told The Independent that the findings of the Delhi serological survey “could be interpreted both as good and bad [news]”.

He explained that “with so many infections happening, and so many people being exposed, it shows that the proportion of people suffering from severe illness or mortality is really small.

“The bad news is that there is still three-quarters of the population that is susceptible. So we should not be lowering our guard – in no way should people think that the disease is so mild or does not make people sick enough so they can stop use of masks or social distancing. We need to keep up these measures.”

At the same time, Dr Lahariya said, the government has yet to release the full data from the survey or any detailed information about its methodology, and that scientists would reserve judgement until the study was published and peer reviewed.

“We really don’t know whether the sample that was taken was representative of the population,” he added, saying more data were need to “give the full picture”.

Dr SK Sarin, director of the Institute of Liver and Biliary Sciences in Delhi which was involve in testing for the survey, said there were two caveats when interpreting its findings. Firstly whether “these antibodies enough to protect you” and second, “whether this survey has included [enough] children, females, the elderly ... these are questions that we cannot answer”.

“For the 77 per cent [who have not been infected], who are they? We need to know what happens to them in the coming months,” he told the Mirror Now news channel. “We should have larger surveys, repeated surveys.”

The gap between the survey data and Delhi’s Covid-19 death count will inevitably raise eyebrows. There have been media reports in the capital of coronavirus deaths being misattributed, and the standard of death reporting as a whole in India is poor.

Dr Jayaprakash Muliyil, an epidemiologist at the Christian Medical College in the southern city of Vellore who is advising the government on virus surveillance, noted that the survey results were only an average, and may not reflect the severity of the outbreak in areas of the city that are worst-affected, such as slums.

“You need to look at different clusters,” he told the Associated Press.

While India’s outbreak was initially concentrated in its largest cities, which have the best health infrastructure and youthful populations, there are concerns that as those hotspots see improvements, the virus is surging in rural areas.

India’s top medical research body, the Indian Council for Medical Research, has asked states across the country to add more labs and enhance their testing capacity.