Bhubaneswar, Feb. 23: Experts of the Regional Medical Research Centre believe that the indigenous circulation of H1N1 virus is causing swine flu here.

While the state has reported three deaths so far, positive swab tests from patients without any travel history has given enough hints that the H1N1 virus is either changing hosts and staying for longer period in the city environment.

Director of the centre Shantanu Kumar Kar said: 'We have done the genetic sequencing of the virus on number of occasions and compared it with the first strain that came to India in 2009 via Pune. While a substantial genetic variation is not seen, it is presumed that the virus stays either in human circulation or in human to animal transmission and causes the menace.'

Kar said the virus could not stay alive in the atmosphere for long, but could stay in dormant state and behaved as common cold virus if it infected people with good immunity. Kar said: 'Persons with compromised immunity are always vulnerable to H1N1 infection. The fluctuations in the weather conditions also helped the virus remain active in this winter.'

Medicine specialist Bidyut Kumar Das said: 'Like the common influenza virus, the swine flu virus changes itself to cope with the environment.'

Since 2009, the virology laboratory at the RMRC has received 694 swab samples, of which 132 were tested positive. It has also formed a repository of all the viral strains to form a bank so that a technical comparison with the genetics of the new strains can be done in the future. The repository will also help the scientists to develop vaccines.

<>Scientist Bhagirathi Dwibedi said: 'From the samples collected at our laboratory, most are coming from Cuttack and Bhubaneswar and the age group of people generally getting affected is above 40.'