The fourth round of the serological survey in Chennai has shown that more than three-fourth of the population aged 6 and above were exposed to SARS-CoV-2 infection and developed antibodies.
For the survey, the Corporation collected samples from 7,026 people in 51 wards covering all 15 zones. The seroprevalence across the zones varied with a minimum of 74.1 per cent in Alandur (zone 12) to a maximum of 82.6 per cent in Royauram (zone 5). The lowest positivity rate was found in Kolathur (ward 65) at 67.2 per cent and maximum positivity was found in ward 71-Otteri (94.7 per cent). Twenty four wards had a positivity rate of above 80 per cent and the majority were in north Chennai. Twenty one wards had positivity rate between more than 70 per cent to less than 80 per cent. Six wards had positivity of less than 70 per cent and the majority were in central and south Chennai. In the first serosurvey conducted in July last year, it was found that one-fifth of the population in the city was exposed to the infection. In the second round conducted in October last year, the findings indicated an overall seroprevalence of around 30.1 per cent with a two-fold rise in adult prevalence between July and October. The third round of the survey conducted by the Directorate of Public Health during February and March this year reported a seroprevalence of 49.2 per cent.