Sero survey in Mumbai: 45% in slums of 3 wards had Covid-19 antibodiesUpdated: Oct 02, 2020, 00:19 IST
Forty-five percent of slum residents and 18% of individuals from other areas surveyed across three city wards were exposed to Sars-Cov2, the virus that causes coronavirus disease (Covid-19), till August’s second half, according to the second phase of the sero survey conducted by the Brihanmumbai Municipal Corporation (BMC), as part of the national study. The civic body said the results indicate that there could be a reduction in the infection’s spread in slum areas.
The sero survey is a study of how many people have antibodies (Immunoglobulin-G) against Sars-Cov-2 in their blood, indicating these people may have been silently infected and recovered, thus helping to map the trend and spread of infection.
The latest survey showed that the virus prevalence in slums went down by 12 percentage points and rose marginally in non-slums, in comparison to the first study in the first half of July. In the first survey, 6,936 samples were collected from R-North (Dahisar, Borivli), M-West (Chembur), F-North (Dadar, Matunga, Wadala), of which 57% samples from slums showed antibodies, followed by 16% from non-slum areas.
The BMC’s second survey, covering the same areas, tested 5,384 people and found 45% samples from slums and 18% from non-slum areas showed antibodies.
Suresh Kakani, additional municipal commissioner in-charge of the public health department of BMC, said, “It is encouraging that in slums, the rate of infection is going down. The number of infected health workers is also less, because of the care they have been taking.”
Even though recent trends show that high-rises across Mumbai are reporting more Covid-19 cases, Kakani said, “In high-rises, there were only 18% people with antibodies, because this survey was done before the Ganesh festival. It was after the festival that our number of cases increased, and people got a chance to mingle with each other.”
The BMC in a statement on Thursday said, “Sero-positivity from the second round indicates there could be a reduction in the spread of infection in slum areas. Marginal increase in sero-positivity of non-slum areas correlates with increase in reported cases in August from non-slum areas.”
According to BMC officials, in the second phase, the sero-prevalence observed among health workers working in slum areas was lower than sero-prevalence in the slum populations (citizens), and this could be due to Covid-19 appropriate behaviour, which includes use of masks and hand hygiene.
The BMC, further in the statement, added, “Emerging scientific evidence hints at fall of antibody levels in recovered or asymptomatic patients over a period of time and might have contributed to the trend between two rounds of sero-survey. The impact of this on immunity, if any, is still unknown.”
Further, the second phase stated that sero-prevalence in women was marginally higher than men in both the rounds, followed by age-wise prevalence, which was comparable to the first round in all ages. In the second round, sero-prevalence in the age group of people above 40 was slightly higher. Sero-prevalence among health workers in both rounds was approximately 27% (as an average).
According to BMC, the second phase of the sero survey was conducted in the second half of August, in which out of a total 5,840 samples, 5,384 participants [92%] were recruited from the general population, while the remaining were frontline workers. In the whole exercise (combining both phases of the surve), a total of 728 health workers were recruited for the study.
Meanwhile, in the second phase, the sampling included people who may have been symptomatic and recovered or asymptomatic. Further, no sampling was done in active containment zones (i.e. during the study period) followed by around 1-2% of the samples belonged to people who had participated in both the rounds.