A Serological surveillance for SARS-CoV2 infection commissioned by NITI-Aayog, Municipal Corporation of Greater Mumbai (MCGM) and the Tata Institute of Fundamental Research (TIFR) has indicated higher exposure of the coronavirus in Mumbai's slums.
As a large cross-sectional survey in India, this study's aim was to estimate sero-prevalence in the population based on random sampling of the general population and health care workers.
In the first round 6936 samples from general population were collected from three wards (R-North, M-West and F-North) in slum and non-slum areas.
Abbott's Chemiluminescence assay (CLIA) tests kits were used to detect IgG antibodies against the coronavirus in the population.
The study was conducted over a 12-14 day period in the first half of July. Participants were from slum and non-slum areas.
Key Findings from General Population
Systematically conducted study estimates around 57% sero-prevalence in slums and 16% sero-prevalence in non-slums, on an average, in the three wards that were studied.
The survey indicates that asymptomatic infections are likely to be a high proportion of all infections, says BMC
High density population density, shared common facilities, may be the factor behind higher prevalence in slums.
The study authors attribute lower numbers in non-slum areas to better physical distancing, better hygiene and other interventions.
It's important to note that these are population surveys and are not 100 percent accurate. The sensitivity (ability to correctly detect COVID-19 antibodies in those tested / true positive rate) and specificity (ability to detect those without the antibodies/ true negative rate) of the test used in the surveys plays an important role. Abbott has claimed their tests have demonstrated greater than 99 percent sensitivity and specificity, 2 weeks after symptoms first appear.
These surveys at best indicate possible spread of the disease in the community and help authorities come up with better strategies. They don't take away the need for continued efforts towards physical distancing, hand hygiene and wearing masks. Nor do they take away the need for robust contact tracing, testing and isolation requirements.
On 28 July, Mumbai reported only 700 new infections. 8776 tests were conducted in a day.
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