Coronavirus: 6 things you need to know about Delhi’s serological survey results

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Published: July 22, 2020 10:25 AM

ICMR is planning to conduct a nationwide serological survey soon to estimate the prevalence of coronavirus infection.

The people surveyed were also divided in two sets—those below 18 years of age and those above 18.

Indicating a large extent of the spread of COVID-19 infection in the national capital, the sero survey commissioned by the Union Health Ministry has shown the presence of IgG antibodies in as much as 22.86% of the people surveyed. The serological survey was carried in Delhi between June 27 and July 10 and a total of 21,387 people were tested in the survey, The Indian Express reported. The result of the survey showed a large number of people who reportedly came in the grip of the coronavirus remained asymptomatic. Let’s take a look at the key findings of the serological survey and the new insights it has brought to the fore in the fight against coronavirus.

What is a serological survey?
Contrary to the PCR-tests being conducted by health authorities to ascertain whether an individual patient has contracted the virus or not, the serological survey is conducted to know the extent of the infection amongst a large population. The survey is conducted by taking the blood samples and then testing the presence of particular antibodies in the blood samples. The presence of antibodies indicates that the person had been exposed to the disease and may or may not have recovered from it. The test has been approved by the Indian Council of Medical Research (ICMR) because of its high sensitivity and specificity.

What does the recent survey conducted in Delhi show?
Out of the total 21,387 people tested in the survey, 22.86% of the samples revealed the presence of antibodies. To put things into perspective, one in five residents in the city has been estimated to have come in the grip of the virus. However, experts have pointed out that the finding cannot be extrapolated over the entire population of Delhi. In other words, the survey is only an estimate and does not tell the actual number of coronavirus cases. Officially, as per the Union Health Ministry data, Delhi has recorded a total of 123,747 confirmed COVI-19 cases as of July 21. Since it is nearly impossible to test every single individual of the population, serological surveys are carried out to know the prevalence of infection. However, it certainly tells that the actual number of coronavirus cases in the capital is many times more than those confirmed by the health authorities.

Which are the worst affected districts?
Out of the 11 districts in Delhi, eight districts revealed the presence of infection at more than 20 per cent. The worst-affected district has been found to be the Central district, with an infection rate of 27.86%. The lowest spread of infection was reported in the South West district (12.95%). The NorthEast and Shahdara districts showed the prevalence at over 27%.

How was the survey conducted in Delhi?
The survey was conducted by the National Centre for Disease Control (NCDC), which comes under the Directorate General of Health Services in the Union Health Ministry. A total of 160 teams comprising four members each—an ASHA/Aaganwadi worker, an auxiliary nurse midwife (ANM), a pharmacist and a phlebotomist—were constituted by the authorities. The antibodies test was undertaken using the Covid Kavach ELISA kits approved by the ICMR.

The teams visited the residents of Delhi at their homes and randomly collected their blood samples. The residential pockets and locations were randomly picked by the authorities across all 11 districts of the national capital. The people surveyed were also divided in two sets—those below 18 years of age and those above 18. Written consent had also been taken from the people before collecting their samples.

How did the government respond?
Taking note of the serological survey findings, the Union Health ministry officials in a press conference said that it was largely due to the efforts made by the government that the prevalence of infection was limited to about 22% of the population. The officials added that despite several dense pockets of population in the city, the infection could be contained due to prompt lockdown, containment measures, contact tracing and other efforts made by the government.

The government also said that about 77 per cent of the population is still vulnerable and susceptible to the virus and continuous efforts should be made to ensure that people wear masks, observe cough etiquette, hand hygiene and physical distancing to stop the spread.

Results of other serological surveys conducted in the country
In April, the ICMR had conducted a similar survey in 83 districts of the country spanning 21 states. The survey had found the prevalence of infection in about 0.73% of people. The infection was a little higher at about 1.09 per cent in the urban areas. However, the survey was conducted at the very beginning of the coronavirus outbreak in the country, during the first phase of the nationwide lockdown. ICMR has said that it would soon conduct a nationwide serological survey to estimate the prevalence of infection at present.

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