The study released Tuesday raises questions over the level of testing in India, which has the third highest number of confirmed cases in the world after the United States and Brazil.
On Wednesday, India reported it had crossed 1.5 million reported coronavirus cases after more than half a million infections were recorded in just 12 days. It took nearly six months for India to reach its first 1 million confirmed cases.
Mumbai, India's financial capital with a population of more than 12 million, has confirmed more than 110,000 cases, including at least 6,180 deaths, according to official statistics. The city is in Maharashtra, the worst-hit state in India with more than 377,000 confirmed cases and at least 14,000 deaths.
The study -- a collaboration between local authorities and medical institutions -- found that 57% of the samples collected from slum residents tested positive for coronavirus antibodies, while only 16% of those living outside of slums tested positive, according to a news release Tuesday.
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