New Delhi: Samples collected from bats in Kerala's Kozhikode and Malappuram districts, where 12 people have died of nipah infection, have tested negative for the virus, according to a report submitted by a central medical team to the Union health ministry on Saturday.

The report has ruled out bats and pigs as the primary source of the nipah outbreak, a health ministry official said. The medical team is now looking into the other possible causes of the outbreak.

A total of 21 samples, including that from seven species of bats, two species of pigs, one bovine and one caprine (relating to or resembling goats), had been sent to the National Institute of High Security Animal Diseases in Bhopal and the National Institute of Virology in Pune.

"These included the samples of the bats which were found in the well of a house in Kerala's Perambra from where the initial death was reported. They have tested negative for the nipah virus," the official said.

Samples from humans suspected of contracting the nipah virus have also tested negative.

"This means there are only 15 confirmed cases, which include 12 deaths. Three persons are undergoing treatment," he said.

The samples from bats found dead in Himachal Pradesh, which were also sent to the Pune institute, have been found negative and the two samples of suspected cases from Hyderabad were negative too.

The health ministry has urged people not to panic, asserting that the outbreak is "localised" in Kerala. It has issued advisories to the general public and healthcare providers to adopt preventive measures.

The multi-disciplinary central team led by the National Centre for Disease Control director is constantly reviewing the situation in Kerala. The team has fine-tuned the draft guidelines, case definitions, the advisory for healthcare workers, information for the general public and advisories for sample collection and transportation accordingly.

The contact-tracing strategy has been successful, the health ministry said, adding that it has been found that all the reported cases, including the suspected ones, had direct or indirect contact with the first casualty or his family prior to contracting the disease.

The central medical team has put Kozhikode and Malappuram on "high alert" and advised authorities to set up facilities to screen suspected cases at the entry and exit points of the districts.

The administration in the two districts has set up a taskforce with a designated control room, and a nodal officer has been appointed to collect data to ensure preventive measures.