In its third sero-survey conducted in the backdrop of COVID-19 to determine antibody response in individuals, the Brihanmumbai Municipal Corporation (BMC) has found a staggering 36.30 per cent sero-positivity among 10,197 citizens selected using "anonymous sampling method" from across 24 wards in the metropolis.
Disclosing the findings of the third sero survey, Mumbai Municipal Commissioner I S Chahal said here on Saturday night: “Overall 36.30 per cent sero-positivity is found in 10,197 blood samples collected from citizens from across all 24 wards. While we found an increase in the percentage of sero-positivity in blood samples taken from non-slum areas, we noticed the decline in sero-positivity in the slums areas”.
“Based on the survey, we intend to accelerate the vaccination campaign in order to limit the spread of the COVID-19,” Chahal said.
The serologic tests measure the antibody response in individuals. Antibodies to COVID-19 are produced over days to weeks after infection with the virus.
The presence of antibodies indicates that a person was infected with the COVID-19 virus, irrespective of whether the individual had severe or mild disease, or even asymptomatic infection.
Surveillance of antibody sero-positivity in a population allows inferences to be made about the extent of infection and about the cumulative incidence of infection in the population.
Among other things, the use of serology in epidemiology and public health research enables understanding of the occurrence of infection among different populations;, how many people have mild or asymptomatic infection, and who may not have been identified by routine disease surveillance, the proportion of fatal infections among those infected and the proportion of the population who may be protected against infection in the future.
The BMC conducted the survey as part of its preventive efforts to limit the spread of COVID-19. “While implementing these measures, it is important to make certain scientific information available regarding the spread of the virus. In this regard, the third sero survey of citizens was conducted in the Greater Mumbai Municipal Corporation area recently,” Chahal said.
In the Serologic tests conducted using unlinked Anonymous sampling method, the BMC found IgG antibodies (sero positivity) in 36.30% of 10,197 blood samples.
While the BMC conducted the first sero-survey of the citizens was conducted in three civic wards in July 2020. It conducted the second survey in three other wards in August 2020. Now the BMC has conducted the third sero-survey in 24 wards across the metropolis.
“For the survey, blood samples collected at municipal dispensaries were tested. The survey also included blood samples collected from private medical laboratories. This sero survey was conducted on blood samples collected from individuals who were not vaccinated,” Chahal said.
“All blood samples have been tested for antibodies at MCGM’s Molecular Biology Laboratory at the Kasturba Hospital.
The findings of the latest sero survey show that there was 35.02 per cent sero-positivity in men, while there was 37. 12 per cent sero-positivity among the women.
“During current sero survey, 41.6% sero-positivity is found in the blood samples taken from municipal dispensaries in slum areas. The first survey found 57 per cent sero-poisitivity in slum areas of 3 wards and during the second sero survey in these 3 ward, sero-positivity was found to be 45 per cent in slums areas,” the survey findings revealed.
According to the findings, blood samples taken from private laboratories in non-slum areas showed sero positivity of 28.5 per cent in the current survey this year. In the first survey, sero-positivity in the non-slum areas was 16 per cent in 3 wards and during the second sero survey, sero positivity was found to be 18% in non-slum areas.
As per the above findings, it is observed that the sero positivity in slum areas is decreasing and that in non-slum areas is increasing. During the second wave of COVID infection, a large number of patients are being detected from non-slum areas. Findings from the survey, therefore, appear to corroborate with the current trend.