Mumbai’s slums have been hit hard by COVID-19. Results of a sero–survey for SARS-CoV2 infection have indicated that 57 per cent of those in the slums tested positive for the infection. Only 16 per cent tested positive in non-slums in the three wards that were studied.
The survey was jointly commissioned by NITl-Aayog, Municipal Corporation of Greater Mumbai (MCGM) and the Tata Institute of Fundamental Research (TIFR). Results of the Delhi sero-survey released on July 9 suggested that 22.86 per cent of Delhi population tested positive for the virus, with certain districts such as Shahdara reporting 27 per cent of the population with the infection.
“Having developed antibodies to SARS-COV2 was no guarantee that the person would be protected against the infection in the future, too. This is because longevity of the antibodies that have been developed against this virus is still being studied as this is a new infection,” Dr Sujeet Kumar Singh, director, National Centre for Disease Control had said at the release of the Delhi results.
The Mumbai study was done in collaboration with Kasturba Molecular Diagnostic Laboratory, Translational Health Science and Technology Institute (THSTI), A T.E. Chandra Foundation and IDFC Institute. As a large cross-sectional survey in India, the study aimed to estimate sero-prevalence in the population based on random sampling methodology; samples were stratified by age and gender, and drawn from the general population and health care workers, and at two time points to infer the spread of the epidemic.
In the first round, 6,936 samples (out of the estimated 8,870) were collected from the general population in three wards (R-North, M-West and F-North) in slum and non-slum areas. Areas under the survey included Dahisar, Matunga, and Chembur. The survey did not include Dharavi.
“Participants were recruited following informed voluntary consent. Anti-SARS-CoV2 lgG antibodies was detected using Chemiluminescence assay {CUA) by Abbott,” the BMC said in an official release. The Delhi sero-survey was done using the indigenous ELISA test developed by the ICMR-NIV.
The study was done in the first half of July, implying that the results indicate the COVID-19 situation in these wards in mid-June, since antibodies take about 14 days to develop. Prevalence in women was marginally higher than in men, the release reads.
What do these results mean? For one, both the Delhi and Mumbai results suggest that asymptomatic infections are likely to be a high proportion of all infections, and hence the reported cases are much lower than the number of infections. In Mumbai, a high prevalence in slums could be attributed to population density and shared common facilities such as toilets and water points.
Concerns around the shared facilities had been raised by the Union health ministry in the early period of the pandemic, particularly during the nationwide lockdown. In its containment strategies, too, the Union health ministry had highlighted that densely populated areas with poor access to healthcare and sanitation facilities were at high risk of spread of infection. In its guidelines on management of COVID-19 in urban settlements in May, the health ministry had said: “These areas are characterized by poor structural quality of housing, inadequate access to safe water, poor sanitation and insecure residential status. There are gaps in health and healthcare services. In the context of COVID (or any other respiratory infectious disease for that matter) implementing strategic interventions such as surveillance, physical distancing, isolation, quarantine and communicating the risk to the dwellers could be challenging.”
On death rate, Mumbai civic authorities have said that the infection fatality rate is low. “Taking together the current prevalence (estimated here) and records from BMC on reported deaths, the infection fatality rate (IFR) is likely to be very low (0.05- 0.10 per cent). Among others, this could be attributed to effective containment efforts and active measures to isolate symptomatic cases by MCGM,” the official statement reads. “Lower prevalence in non-slums could be due to better social distancing and access to better hygiene in addition to intervention by Municipal Corporation of Greater Mumbai to stem the spread of infection.”
