Urgent global action is needed to prevent the spread of a multi-drug-resistant "superbug" after it was found in water supplies in the Indian capital, doctors said in research published Thursday.
The study in The Lancet medical journal said that New Delhi metallo-beta-lactamase 1 (NDM-1) producing bacteria were found in 51 out of 171 samples taken from water pools and rivulets and two out of 50 tap water samples in the city.
NDM-1, first identified in 2009, is a gene that enables some types of bacteria to be highly resistant to almost all antibiotics.
Positive samples included those collected in and around the commercial and business hub of Connaught Place and the Red Fort area.
"International surveillance of resistance, incorporating environmental sampling as well as examination of clinical isolates needs to be established as a priority," the team from Cardiff University in Britain wrote.
Mohammed Shahid, from the Jawaharlal Nehru Medical College and Hospital in India's northern Uttar Pradesh state, added that potential for a wider, international spread of the superbug was "real and should not be ignored."
"Coordinated, concrete, and collective efforts are needed, initially to limit widespread dissemination, and finally to combat this emerging threatening resistance problem," Shahid said.
The researchers conducted the study in September and October last year, soon after warning that the superbug could be spread by foreign nationals coming to India for medical treatment.
At the time, the Indian government dismissed the research as scaremongering and criticised the naming of the bug after the Indian capital.
But the World Health Organization later called for monitoring after cases of infection were reported around the globe.
In the latest study, the researchers said the presence of NDM-1-producing bacteria had "important implications" for New Delhi residents who were reliant on public water supplies and sanitation.
NDM-1 was found in the bacteria that cause cholera and dysentery, lending weight to the theory that it was not solely a hospital-acquired infection but present in the environment.
The research suggested that the transfer of NDM-1 between different bacteria was highest at 30 degrees Celsius (86 degrees Fahrenheit) - within the range of temperatures in New Delhi for seven months of the year.
"This period includes the monsoon season, when floods and drain overflows are most likely, which potentially disseminates resistant bacteria," the authors said.
"Oral-faecal transmission of bacteria is a problem worldwide, but its potential risk varies with the standards of sanitation.
"In India, this transmission represents a serious problem - 650 million citizens do not have access to a flush toilet and even more probably do not have access to clean water."
The authors said it was unclear whether the data could be applied to other Indian cities but there was an "urgent need" for follow-up studies, including in Pakistan and Bangladesh, which have also been identified as sources.