New Delhi, July 27 - Screening of air passengers at exit points from a swine flu infected country is impractical, a US health expert said Monday.

'Exit screening is impractical. No one can stop the movement of the virus at this point of time,' Dan Rutz, global health communication team leader of Centre for Disease Control and Prevention (CDC), told IANS.

'A person might have contracted the virus much before showing symptoms. Here, exit screening wont help. You cannot stop people's movement,' Rutz, who is here now, said.

The Indian government has appealed to countries to carry out exit screening before allowing passengers to board a flight to India.

Rutz said in the US, over a million people have now been infected by swine flu.