The samples of 15 suspected cases of H1N1 flu were found to be negative even as the results of five more persons are awaited.
While the samples of three suspected persons from Delhi have tested negative, the results of two from Cochin are still awaited and two more suspected cases have been placed under isolation in Bangalore, Joint Secretary of Ministry of Health Vineet Chaudhary told reporters in New Delhi on Tuesday.
Another person in Delhi had come forward on his own to the Ram Manohar Lohia hospital and he is also been checked for the virus.
Chaudhary said around 30,000-40,000 people were being screened regularly at the airports.
He divulged that one suspected case who later turned out to be negative was tracked down to Andhra Pradesh after a tip off from the Chinese government.
The 27-year-old man had taken a flight from Mexico to Shanghai and took an Indian carrier back home. Authorities in Shanghai had found a positive case of H1N1 flu in the flight from Mexico following which they informed the Indian embassy in Beijing and thus this man was tracked down within 24 hours.
In another development, some states in Maharashtra have informed the Centre that while there are no cases of H1N1 flu in their region, some pigs are afflicted with swine fever and that is why they are being culled.
"Swine fever as such cannot be transmitted to humans, though it can cause mortality in pigs," Chaudhary said.