Twenty-two per cent of the people who took part in a serosurvey in Bengaluru Urban in September had antibodies indicating past infections while 9.2% had active infections. In all, the Covid-19 prevalence rate in Bengaluru stood at 29.8%.
The serosurvey, held in September, covered 3,617 samples.
The BBMP's western zone had the highest prevalence at 45.6%, followed by South (38.9%). Out of the 405 samples tested in the West Zone, 35.1% had antibodies and 13.2% an active infection. In the South Zone, out of the 422 samples tested, 29.9% had antibodies and 10.7% an active infection.
Dr Manoranjan Hegde, Health Officer, BBMP, West Zone, said: "The West Zone is a thickly populated area with a number of slums. Right from the start of the pandemic, the West Zone has been reporting the most cases among all eight zones. Earlier, Chamarajpet and Chickpet were problematic areas. Now, most cases are being reported from Malleswaram, Rajajinagar and Mahalakshmipuram. A majority of the primary contacts of Covid patients have tested positive. Tracing and testing are the only strategies for containment."
Munish Moudgil, Special Officer for South Zone, said: "South zone cases peaked in July and August, that is why a higher percentage of people were found to have antibodies in the serosurvey. The number of cases in Mahadevapura is rising now when previously South and West zones were peaking. Contact tracing has to be strengthened and the wearing of masks should be followed diligently."
The BBMP Covid bulletin on November 4 showed that over the past 10 days, Mahadevapura contributed to 19% of the cases, followed by South and East at 15% cases each.
But four out of the eight BBMP zones surveyed also have a low case-to-infection ratio (Bommanahalli, East, West and South), which suggests that the strategy employed for testing is reasonable and can be replicated in other districts, the study said.
The surge in cases is yet to occur in the districts with the lowest estimated prevalence of Covid-19 like the BBMP's Mahadevapura zone with 14% prevalence, researchers involved in the serosurvey said. Out of the 433 samples tested here, 7% had antibodies and 7.2% an active infection.
The Mahadevapura zone has a large number of migrant construction workers and hence the cases are likely to surge. The BBMP's November 1 war room report showed that the South Zone had 22.6% of cases with zero contacts. This shows that the zone is struggling to trace contacts.