The samples of four close contacts of the 12-year-old kid who succumbed to Nipah virus infection last week has returned negative, but the source was yet to be identified and the government was according to top priority to it, Kerala health minister Veena George said here on Sunday.

"The sample testing is also continuing in the epicenter of the infection," the minister told the media. She said it was important to identify the source of infection and the surveillance team from the National Institute of Virology, Pune, has been collecting samples from various areas. "The high-risk contacts have been isolated in the Kozhikode Medical College Hospital. Their health condition is stable. It's important that we identify the source of the infection. We are trying to. The Pune NIV team is collecting samples from various parts to identify the source," she said.’

 The state government had conducted a complete house-to-house survey within a three-km radius from the house of the 12- year-old boy who succumbed to Nipah virus on September 5 as part of its fever surveillance.

The govt earlier had declared that around 15,000 houses from the containment zone were included in the survey and details were sought from around 68,000 people.