Second round of serological survey to begin next week

The second round of serological survey to test the prevalence of the coronavirus disease among Gurugram’s residents will be held next week, health department officials

The second round of serological survey to test the prevalence of the coronavirus disease among Gurugram’s residents will be held next week, health department officials said on Friday.

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The survey is being conducted to detect unreported cases as the person may have been asymptomatic and did not know they had contracted the virus. In the survey, a test called enzyme linked immunosorbent assay (Elisa) will be used to detect antibodies that the body’s immune system produces to combat the Sars-CoV-2 virus that causes the infection.

The first round of 182 such tests were done by June 24 that found 32 persons positive.

“We were given 460 ELISA kits, and still have 278 left. Most, if not all, will be used in the next survey exercise that will likely be held from Tuesday. We may also start on the weekend itself if preparations can be made,” said Dr. Ram Prakash, district epidemiologist. He added that the health department has begun compiling a list of individuals from whom blood samples will be sought.

The tests will not be conducted at random

“There are 20 categories that the Indian Council of Medical Research (ICMR) guidelines recommend for serological studies, from healthcare workers, frontline workers, people with compromised immunity, and those who have already had the disease before. We will be conducting the tests across the district, with some focus on large outbreak regions,” said Prakash.

Experts explained that seropositive diagnoses are not helpful in determining the extent or severity of a patient’s infection, but is a valuable epidemiological tool to determine the prevalence of a disease within a community. An ICMR study conducted in 75 districts across the country, for example, found that less than one percent of the population – 0.73% - in non-containment zones had developed antibodies.

However, such data has not yet been extrapolated in Gurugram. “A sample size of 182 people will not really give us a clear picture of prevalence. It is too small. We will take the reports from all 460 kits and analyse them to see how much of the district’s population has developed antibodies. By extrapolating the data, we would be able to say, with reasonable certainty, the total number of people who have been infected with SARS-Cov-2 in Gurugram,” said Prakash.

According to Dr. Prabhakaran Dorairaj, vice president of research and policy at the Public Health Foundation of India, however, even 460 is quite small. “Even if the right kinds of subjects are selected, it will not adequately represent the whole of Gurugram’s population. If the goal is to get a correct picture of prevalence, then the department must first classify the district into two areas: old Gurugram and new Gurugram. Within these areas, you have to use socio-economic data at the ward level and census enumeration block level to create a sample representative of the larger demography of the city. That will tell you how prevalent the disease really is in Gurugram,” he said.