By Kaushik Swaminathan, New York Times

NEW DELHI — The health authorities in the southern Indian state of Telangana have issued a high alert in Hyderabad, the state capital, after finding a strain of polio in sewage water there, a state health official said Wednesday.

A polio vaccination drive began Monday, the health authorities said, with the aim of vaccinating about 300,000 children in parts of Hyderabad and in the Rangareddy district also part of the state of Telangana, according to a statement from India’s Ministry of Health and Family Welfare. The Hyderabad metropolitan area has more than 7.7 million people and the Rangareddy district 5.2 million, according India’s 2011 census.

“We have to avoid any kind of risk, even though nobody has been affected,” said Rajeshwar Tiwari, the principal secretary for the Ministry of Health in Telangana. “We want to remain a polio-free nation.”

India was declared free of polio in 2014 after having no new cases over three years. The country’s polio vaccination program, in which health workers fanned out across the country to reach millions of children, is widely considered a great success. Polio vaccination rates for India’s children reached more than 90 percent, said Nicole Deutsch, the director of polio operations for UNICEF India.

Detecting the virus in sewage water is a concern because it could lead, in rare cases, to an infection in a child who has not been vaccinated.

The polio virus was found in 14 sewage samples from different parts of the country from January 2015 to May of this year, the Ministry of Health said Wednesday. The strains came from the excretions of vaccinated children and were therefore much less infectious than other forms, experts say.

The new effort in Hyderabad will inoculate for all strains of the polio virus as a precautionary measure, according to the Ministry of Health’s statement. In April, there was a global shift from immunizing against one of those strains, which had not been detected in India since 1999, Deutsch said.

Because no one has yet been afflicted with the strains of the disease found in the sewage water, India will retain its status as a polio-free country, experts said.

“India continues to be polio free,” the Ministry of Health said in its statement.

Deutsch said that transmission from the type of polio strain found in the sewage system was “extremely, extremely rare.”

“Almost all the cases of infection have been with compromised children that haven’t been immunized,” she said.

The polio strain was found in a sewage treatment plant in a suburb of Hyderabad called Amberpet, Tiwari said.

He said that the Indian authorities contacted the World Health Organization and UNICEF after the sample tested positive this month.

Nida Najar contributed reporting.

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