Director General of Communicable Diseases I Nyoman Kandun said the possibility of re-assortment between the avian influenza virus and other flu viruses was always possible, but had not yet happened.

"When and where it will happen, nobody knows. Risk assessment therefore is very important," Kandun was quoted by the Jakarta Post as saying Thursday.

Re-assortment of the highly pathogenic avian influenza and seasonal flu virus would give birth to a "new" virus that could be easily transmitted from human to human, resulting in a pandemic.

Scientific journal Cidrap has quoted researcher Vivi Setiawaty of the Center for Biomedical and Pharmaceutical Research and Development as saying a 16-year-old Indonesian girl died of co-infection between seasonal and avian strains of influenza in April2007.

The girl tested positive for flu under the Health Ministry's flu-surveillance system, which was established in 2005 shortly after the country reported its first bird flu infection in a human.

The girl had shown flu symptoms for several days before she was treated for an infectious disease in East Jakarta. She was reported to have mild symptoms, including sore throat, cough and body aches, but displayed neither respiratory problems nor signs of pneumonia.

Cidrap said the girl's case occurred within the period when the Indonesian government ceased sharing flu isolates with the international laboratory overseen by the World Health Organization.

"Such infections are of great concern due to the possibility of genetic re-assortment leading to the emergence of a H5N1 strain that is more easily transmitted human to human, and emphasizes the importance of advanced laboratory-based surveillance in geographic regions where both human and avian influenza viruses are co-circulating," Cidrap reported.

Asked about the finding, Kandun said Indonesia needed to strengthen its surveillance system, including laboratory capacity.

I Gusti Ngurah Mahardhika, a virologist and microbiologist at Udayana University in Denpasar, said the co-infection involving the girl most likely was not the first such case in Indonesia because researchers used to focus only on H5N1 and did not check for the presence of other H viruses.