NEW DELHI — The devotees came by the thousands from all corners of India and beyond, converging on a large white complex in a crowded quarter of Delhi to share a message of piety.

When they left in the first weeks of March, they unknowingly carried the coronavirus with them.

Gatherings last month at the headquarters of a prominent Muslim missionary group are emerging as India’s first “super-spreader” event, complicating efforts to control rising infections in this nation of 1.3 billion people.

More than 400 confirmed cases and at least 10 deaths across the country — stretching from Tamil Nadu in the south to Kashmir in the north — have been linked to people who attended events at the Tablighi Jamaat center near a historic shrine in India’s capital.

The infections, which represent about a fifth of India’s total cases, have sparked a frantic effort to track down anyone who attended the recent meetings. In at least two states, potential contacts are being traced using mobile-phone location data.

The outbreak also has provoked a spasm of Islamophobia in India, a Hindu-majority nation that is home to 200 million Muslims. In February, the country witnessed its deadliest sectarian clashes in years after the government’s pursuit of a controversial citizenship law sparked violence.

As the pandemic continues, people practicing their faith have become unwitting but powerful vectors in the spread of the virus. A cultlike church helped fuel the pandemic in South Korea. A synagogue north of New York City was at the center of an early outbreak. An evangelical congregation in France was the source of hundreds of infections.

India closed the headquarters of a Muslim missionary group March 30 to investigate claims that dozens were infected by the coronavirus at the group's meetings. (Reuters)

India banned all religious gatherings when it instituted a three-week nationwide lockdown March 25. But several states and cities already had implemented their own restrictions: Delhi, for instance, prohibited all assemblies of more than 50 people March 16.

The activities of Tablighi Jamaat have emerged as a particularly potent vehicle for transmitting the virus. Founded in India nearly a century ago, the group has as many as 80 million adherents worldwide. It is built around small bands of itinerant missionaries who urge fellow Muslims to deepen their observance and model their lives directly on the ways of the prophet Muhammad.

The group eschews politics and in theory operates without formal record-keeping, said Barbara Metcalf, a prominent historian of South Asian Islam. It stresses proselytizing and travel, producing a “state of vulnerability and uncertainty in which one learns to be dependent on God,” Metcalf wrote.

The Tablighi Jamaat cases in India may be linked to another religious gathering held by the same group in Malaysia. At the end of February, 16,000 people from numerous countries attended a multiday Tablighi Jamaat event at a mosque in Kuala Lumpur. That gathering was the source of hundreds of coronavirus cases in Malaysia and dozens more in Brunei, Cambodia, Singapore, Sri Lanka and Thailand. Cases have also emerged at a Tablighi center in Pakistan.

By early March, missionaries from several Southeast Asian countries were in India. Nearly all of them passed through the bustling complex in Delhi’s storied Nizamuddin district and then traveled on to different parts of India. Several of them later died, including a Filipino man and six Indonesians. One Indian who went home to Kashmir after participating in a three-day event at the Delhi center also died.

Missionaries and devotees continued to arrive at the center even after Delhi authorities banned large gatherings. Then India suspended all passenger trains March 22, followed swiftly by the countrywide lockdown. 

About 2,300 people were stuck at the Tablighi Jamaat headquarters, unable to leave or travel. Yet the authorities took no action to remove them until this week, when all of those at the center were shifted to quarantine facilities or hospitals.

“Everybody now wishes that [activities] had been discontinued earlier,” said Fuzail Ayyubi, a lawyer representing the Delhi center, adding that the group had communicated its situation to the authorities and cooperated with the police.

“This is not the right time to blame us or the government,” Ayyubi said. “Everybody is stuck in a situation mankind hasn’t seen before.”

Local authorities across India are racing to contain the outbreak, sometimes using methods that appear to be without precedent here. In Kashmir, a restive Muslim-majority region, the government compiled a list of more than 800 residents who were present earlier in March in Delhi, including in the neighborhood where the Tablighi Jamaat center is located.

The list was assembled with the help of telecom companies after an analysis of data from cellphone towers, call records and travel itineraries, said a senior police official in Srinagar, who spoke on the condition of anonymity because he was not authorized to discuss the matter with the media.

Three other officials and doctors in Kashmir confirmed they had received instructions to check on the health of the individuals mentioned on the list. The Washington Post reviewed a copy and contacted 10 people listed. All confirmed they had recently been either near the Tablighi Jamaat center or in another Delhi neighborhood frequented by Kashmiris.

Kashmir has been subject to a broader crackdown since last August, when India stripped the territory of its autonomy and statehood. Rohit Kansal, the top bureaucrat in Jammu and Kashmir, did not confirm or deny that the region was using cellphone data in its effort to trace contacts. The territory is “following a proactive and aggressive policy of test and trace,” he said.

In the southern state of Tamil Nadu, authorities say that about 1,100 residents traveled to the Tablighi Jamaat headquarters in March. Many of those have come forward, and the state is using a “multitude of methodologies,” including “clustering of cellphone data,” to trace people, said Beela Rajesh, the state’s health secretary.

The Indian government has expansive authority to require mobile-phone operators to share data. While the Supreme Court ruled in favor of a right to privacy in 2017, its legal contours remain unclear.

Indian officials are increasingly looking to cellphone data to help enforce measures to control the pandemic. Arvind Kejriwal, the top elected official in the state of Delhi, announced Wednesday that the local government would temporarily use cellphone data to determine if more than 20,000 people were violating orders to quarantine themselves at home.

Some Indian Muslims worry that the infections linked to the missionary group will intensify anti-Muslim rhetoric. The cases can be used as “a convenient excuse for some to vilify Muslims everywhere,” wrote Omar Abdullah, a senior politician in Kashmir. One prime-time anchor referred to the coronavirus cases as “a murderous attack in the name of faith,” and “CoronaJihad” trended on social media.

The first-known Indian victim of the outbreak at the Tablighi center was Mohammad Ashraf Anim, a 65-year-old Kashmiri businessman. He had traveled to Delhi to take part in a special three-day quarterly event for devotees, said a person familiar with his plans who spoke on the condition of anonymity. Anim returned home to Kashmir and attended prayers at a mosque the following Friday. A few days later, he developed coronavirus-related symptoms. He died March 26.

Irfan reported from Srinagar.