The National Institute for Communicable Diseases has admitted it is concerned about the possible spread of swine flu in South Africa.

The institute's Barry Schoub said winter conditions appears to weaken the immune system?s ability to fight disease, making it easier for people to become infected.

Last week health officials confirmed a 12-year-old American boy who came into the country was infected with the H1N1 virus.

He is currently recovering in isolation. The NICD is trying to track down people who may have come into contact with him during the flight from Atlanta.

"It [swine flu] has spread widely throughout the world. There is a lot of seasonal flu around so that kind of environment does promote the spread of influenza. So there is quite a big chance that we may well have more cases," Schoub remarked.