(Updates with details)

MUMBAI/NEW DELHI, Aug 18 (Reuters) - India's interior minister Amit Shah was hospitalised again on Tuesday after complaining of fatigue and body ache, four days after he said he had recovered from COVID-19, as cases in the country surged to more than 2.7 million.

Shah, a close aide of Prime Minister Narendra Modi and the virtual number-two in his cabinet, was admitted to the government-run All India Institute for Medical Sciences in the capital New Delhi, the hospital said in a statement.

"He is comfortable and continuing his work from the hospital," it said, adding he had now tested negative for COVID-19.

Shah is the highest-profile Indian politician to have been infected with the coronavirus. On Monday, Kiran Mazumdar Shaw, the head of pharmaceutical company Biocon Ltd that makes COVID-19 medicines, said she too had tested positive.

India has reported the world's third-largest number of infections after the United States and Brazil, with cases topping 50,000 every day since July 30. India's cases jumped by 55,079 on Tuesday, while deaths rose by 876 to a total of 51,797.

Cases have largely stabilised in Mumbai and Delhi, but there has been a steady rise in smaller cities such as Pune and Bengaluru.

Authorities in the education and autos hub of Pune, to the south of Mumbai and home to 3.5 million people, said late on Monday that 51.5% of the people surveyed in five of its worst affected areas had shown the presence of antibodies, indicating that the spread of the virus was higher than reported.

"This is the only reliable information about the magnitude of infection in the country," said T Jacob John, a retired professor of clinical virology at Christian Medical College in Tamil Nadu state.

"The antibody surveys are telling you that the actual infection burden has been several times larger than the antigen and RT-CPR tests have shown." (Reporting by Devjyot Ghoshal and Shilpa Jamkhandikar; Additional Nigamananda Prusty; Editing by Kim Coghill and Muralikumar Anantharaman)