LONDON—A gene that can turn many types of bacteria into deadly superbugs was found in about a quarter of water samples taken from drinking supplies and puddles on the streets of New Delhi, according to a new study.

Experts say it's the latest proof that the new drug-resistance gene, known as NDM-1, named for New Delhi, is widely circulating in the environment — and could potentially spread to the rest of the world.

Bacteria armed with this gene can only be treated with a couple of highly toxic and expensive antibiotics. Since it was first identified in 2008, it has popped up in a number of countries, including the United States, Australia, Britain, Canada and Sweden.

Most of those infections were in people who had recently travelled to or had medical procedures in India, Pakistan or Bangladesh.

“This is not a problem that is looming in the future ... there are people dying today from infections that can't be treated,” said David Heymann, chairman of Britain's Health Protection Agency. He was not linked to the research.

Last fall, British scientists analyzed more than 200 water samples from central New Delhi, including public tap water and water that collected in the streets. They found the superbug gene in two of the drinking water samples and 51 of the street samples. Researchers found the gene in 11 different types of bacteria, including those that cause dysentery and cholera.

As a comparison, the scientists also took 70 water samples from a water treatment centre in Cardiff, Britain. No superbug genes were found in any of those. The research was paid for by the European Union and was published online Thursday in the journal Lancet Infectious Diseases.

Mark Toleman, a senior research fellow at Cardiff University and one of the study authors, said the superbug gene was being spread through New Delhi's water supply, but that experts didn't know how many people were being sickened by it. He guessed about a half million people in New Delhi are now carrying the superbug gene naturally in their gut bacteria.

Indian officials called the study “unsupported” and denied the gene was a public health threat. They cited a random sample of nearly 2,000 women in a New Delhi hospital which they said showed no sign of it.

“We know that such bacteria with genes are in the atmosphere everywhere,” said V.M. Katoch, director-general of the Indian Council of Medical Research. “This is a waste of time,” he said. “The study is creating a scare that India is a dangerous country to visit. We are condemning it.”

Since the superbug gene was found in the U.K. last year, British officials say there have been about 70 cases of it in the U.K. including a small hospital cluster.

“We have a vested interest in sorting out sanitation problems in India,” Toleman said, adding the West should invest more money in clean water projects in Asia. “Otherwise (superbugs) could filter out from Asia and will spread through the world.”

Other experts weren't sure how prevalent the NDM-1 gene would become but were preparing for the worst.

“It's like asking in the 1980s if a few HIV cases should be a big worry,” said Guenael Rodier, director of communicable diseases at the World Health Organization's office in Copenhagen. “The fact that (NDM-1) has emerged is worrisome, but forecasting what it will do is very difficult.”

He explained that was because resistant strains sometimes mysteriously disappear.

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In an accompanying commentary, microbiologist Mohd Shahid of India's Aligarh Muslim University wrote that more studies are needed in India to assess how threatening the superbug problem is.

“The potential for wider international spread ... is real and should not be ignored,” he wrote.

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