More than half the residents of slums in three areas in India’s commercial capital, Mumbai, tested positive for antibodies to the coronavirus, a new survey has found.

Only 16% of people living outside slums in the same areas were found to be exposed to the infection.

The results are from random testing of some 7,000 people in three densely-packed areas in early July.

Mumbai has reported more than 110,000 cases and 6,187 deaths as of 28 July.

The survey was carried out by the city’s municipality, the government think-tank Niti Aayog and the Tata Institute of Fundamental Research.

It found that 57% of the people tested in slum areas of Chembur, Matunga and Dahisar had been exposed to the novel coronavirus.

Some 1.5 million people live in these three areas located in the western, eastern and central parts of the city.

Scientists involved with the study told the BBC that the results pointed to a number of things about the prevalence of the infection in one of India’s worst-hit cities.

For one, the virus has spread more widely than was earlier believed in the city’s slums, where more than half of Mumbai’s 12.5 million people live.

Scientists believe the sample tested was “statistically robust” and representative.

“The three areas we chose for the tests had a varying number of reported coronavirus infections, and they were a mix of slums and stand-alone houses and housing complexes. The idea was to see whether population density was driving changes in the prevalence of infection,” Dr Ullas S Kolthur of the Tata Institute of Fundamental Research (TIFR) told the BBC.

Scientists say the survey does not claim to be representative of the prevalence of the coronavirus infection in the entire city – it was carried out in three of the 24 “wards” or administrative unit areas.

“But we believe the prevalence rate in other areas should not be terribly far away from the numbers in the survey,” Dr Sandeep Juneja, who is also at the TIFR, said