Coronavirus update | A fifth of Chennai's population exposed to COVID-19: Sero survey

One-fifth of the population in Chennai has been exposed to COVID, a sero survey for the transmission of the coronavirus infection in Greater Chennai Corporation (GCC) areas revealed. "Overall, one-fifth of the population in Chennai has been exposed to SARS-CoV-2 (the virus, severe acute respiratory syndrome coronavirus 2) infection," the GCC said in its preliminary finding.

The sample size was around 12,000 to detect a sero prevalence of 2 percent, for a relative precision of 20 percent design effect of 2.5 and for 95 percent confidence interval.

Of the individuals tested, 2,673 individuals had evidence of past SARS-CoV-2. "The reading (inference) is 21.5 pecent of Chennai's population reached the immunity levels by July-end," GCC commissioner G Prakash told reporters.

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"Now, the (immunity) levels will be more and it would also mean a (comparatively) lower transmission rate," he said adding the scientific study would be useful to alter strategies to tackle COVID here.

Around 80 percent of the population is still susceptible to SARS-CoV-2 and "we need to understand the reasons for varying sero prevalence across zones to improve our control measures," the civic body said.

"There is huge variation in seroprevalence across zones ranging between 7.1 per cent in Madhavaram and 44.2 percent in Tondiarpet."

The infection to case ratio is lower compared to some of the published studies (Santa Clara, National survey) - indicating high testing performance. The field data/sample collection activities happened between 18 and 28 July and the testing of the samples was completed by August 6, the GCC said in an official release adding the mean age of individuals surveyed was 41.1.

The serosurvey was conducted in the GCC areas to estimate the proportion of the population exposed to SARS-CoV-2. The study design was a multi-stage cluster sample survey among individuals aged more than 10 years.

Tamil Nadu on September 1 reported 5,928 new COVID cases pushing the tally to 4,33,969, while the death toll stood at 7,418 with 96 more fatalities. Out of the over 5,900 new infections, the state capital shared 1,084 and the remainder was scattered across Tamil Nadu.

The state tally of 4.33 lakh plus positive cases till date includes Chennai's 1,36,697 infections.

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