57% in slums, 16% in societies exposed to Covid-19: Mumbai sero-survey

Health workers wear protective gear on their way to take health details of the residents of a 'containment zones' at the Kajupada area in Mumbai
According to the findings of a sero-survey conducted by the Brihanmumbai Municipal Corporation (BMC) 57 per cent respondents from slums were exposed to and had developed antibodies against SARS-CoV-2 virus, while the figure for residential societies stood at 16 per cent. The survey was conducted on 6,936 people from three wards, reports The Indian Express.

Explaining higher exposure to the virus among slum residents (nearly 3.5 times), officials associated with the survey said conditions such as shared toilets, high population density and lack of physical distancing could be responsible.

The study further found that more women had been infected compared to men while, overall, 40 per cent had had the infection.

Fatalities in slums were not high despite the high exposure. “This could be due to multiple factors. We have to look at demography, and low fatality rate could also be due to a possible higher percentage of younger population in slums,” said Dr Ullas Kolthur Seetharam, from Tata Institute of Fundamental Research (TIFR), who was part of the study.

None of the respondents had taken a RT-PCR test for Covid-19. This implies they were either aysmptomatically infected or may not have had serious enough infections.

The study took place over a fortnight in July in Dahisar, Chembur and Matunga.

The survey was conducted by BMC along with TIFR and Niti Aayog. Among the respondents there is an equal mix of slum and non-slum dwellers, men and women, and people from different age groups, and from ages 10 and above. Officials said this was more representative of the population under observation, unlike tests by private labs.

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Out of the targeted 8,870 people, 6,936 were eventually tested.

“Close to 40 per cent tested positive over all. The results have shown that asymptomatic population of Covid-19 is higher than we expected, which is a good news. People have been exposed to the coronavirus and most have not even developed symptoms,” said Suresh Kakani, additional municipal commissioner.

Kakani added that preventive measures like use of masks and sanitising hands will be continued. “This also shows our strategy on testing and isolating in slums has worked. We lifted the entire high risk population and quarantined them. This helped break the viral chain,” Kakani said.

Residential areas, on the other hand, had lower exposure rate due to individual rooms with toilets, said Seetharaman from TIFR. “There is more intermingling of population in slum,” he said. A second sero survey will be conducted after a month to measure epidemiological changes.

Last week, data collected for 9,590 samples and tested for antibodies in Mumbai’s two private labs had shown 24.3 per cent had antibodies to battle Covid-19. The samples for this test were collected from businesspersons, salon staff, office-goers and health workers. This indicates that close to one-fourth of Mumbai's population have already been exposed to the coronavirus and have generated antibodies against it.

The BMC sero survey, however, indicates a higher exposure of the population to Covid-19. According to experts, private labs tested more people from residential areas. These respondents can afford testing. The positivity rate of antibodies in this section of the population is lower than that found in slum dwellers, With the latest survey by BMC now covering slum settlements, the exposure rate has risen.

Last week, a sero-survey study done in Delhi found that 23.48 per cent of the city's respondents had IgG antibodies. The study was conducted by the National Center for Disease Control (NCDC) in collaboration with the Delhi government from June 27 to July 10.

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