One-fifth of Chennai's 87 lakh plus population has been exposed to SARS-CoV-2, the virus that causes Covid-19, while around 80 percent of the population is still susceptible to the infection, according to a sero-survey conducted by the Greater Chennai Corporation (GCC).
The survey conducted in the months of July and August has revealed a “huge variation” in seroprevalence across zones, while showing that infection to case ratio is lower compared to some of the published studies, indicating high testing performance.
With a sample size rounded to 12,405, the serosurvey was conducted in 51 of the 200 wards under the GCC limits which were chosen by population proportion to size method after which six streets were chosen from each ward by simple random sampling method.
The report says that the infection to fatality ratio is comparable or lower to published studies while noting that around 80 percent of Chennai’s population is still susceptible to SARS-CoV-2 infection.
Chennai, which is one of the worst-affected cities in the country due to the coronavirus, joins others like Delhi and Pune to conduct sero-surveys to study the prevalence of the virus. At last count on Tuesday evening, Chennai had reported a total of 1,36,697 cases including 1,20,820 discharges and 2,770 deaths. The active cases stood at just 13,107.
The samples were tested for IgG antibodies against SARS-CoV-2 using Abbott Architect SARS-CoV IgG CLIA and blood samples from 12,405 individuals from 51 wards covering all the 15 zones were collected.
“Of the 12,405 individuals tested, 2673 individuals had evidence of past SARS-CoV-2, with an unweighted seroprevalence of 21.5% (95% CI: 20.8%-22.2%). There is huge variation in seroprevalence across zones ranging between 7.1% in Madhavaram and 44.2% in Tondiarpet,” the survey said.