The Centre for Health Protection is investigating an imported case of H9 influenza A infection involving a 47-year-old Guangdong woman.

She came down with breathlessness and a cough October 26. She came to Hong Kong for medical treatment and was admitted to Queen Mary Hospital October 28. She is stable and staying in isolation.

She had an underlying medical condition requiring regular medication. Her family members have been put under medical surveillance.

As she was in Guangdong during the incubation period, the centre has informed health authorities there and the World Health Organisation, the Ministry of Health and Macau's health authorities of the development.

H9 Influenza A is a mild form of avian flu. Infection in humans is rare.

This is the sixth time H9 viruses have been found in humans in Hong Kong. Four girls and a boy were confirmed to have suffered from H9 infection in 1999, 2003, 2007 and 2008.

People should avoid contact with live poultry to minimise the chance of being infected with avian flu.