The Agriculture, Fisheries and Conservation Department (AFCD, http://www.afcd.gov.hk/) of the government of Hong Kong recently reported outbreaks of avian influenza in two chicken farms in Hong Kong (1), as well as sporadic infections in wild fowl found dead in Hong Kong (2). As a result, control measures have been implemented. These included the slaughter of around 16 000 chickens, closure and disinfection of one of the live poultry markets which had contact with the farms and the halting of imports of chickens from mainland China (3). The virus has been partially typed and found to be influenza A (H5). The virus is not the same strain of influenza A (H5N1) (4) that crossed over to humans in 1997, causing six fatalities (5). Outbreaks of avian influenza due to influenza A (H5N1) viruses occurred in poultry in Hong Kong in May 2001 and February 2002, resulting in culls of about one million chickens on each occasion. Neither of these outbreaks was associated with transmission to humans. The last reported incident of transmission of avian influenza (H9N2) to humans was in 1999 in two young children in Hong Kong and the resulting illness was reported to be mild and self limited (6).

After the poultry outbreaks in February 2002, the Hong Kong authorities initiated a pilot vaccination programme in 21 chicken farms in one area of the territory. In light of the recent outbreak, a decision has been taken to expand the vaccination programme to more farms in the vicinity (7). Strict licensing conditions are also enforced at chicken farms (there are 157 chicken farms in Hong Kong) by the AFCD. These include prohibiting sales direct to retail outlets and improving sanitary conditions with disinfection facilities (8). The AFCD also conducts routine random virological testing of chickens and monitors health conditions of chickens closely.

The demand for freshly slaughtered poultry in Hong Kong outstrips supply and so there is the continued importation of chickens from mainland China, where poultry farming is not so strictly licensed and regulated. This means that the risk of outbreaks of avian influenza in Hong Kong is likely to remain. The major concern is the possibility of a recombination of an avian influenza virus with another human or animal influenza virus creating a virus which is more adapted for human to human transmission, or a mutation of the existing avian viruses which makes them more transmissible to humans. Genetic analysis of the strains from the outbreaks in May 2001 and February 2002 has shown that they differed from those that caused the human fatalities in 1997 (9). It has been suggested that the close relationship between the human populations in southern China (including Hong Kong) and domestic animal populations such as poultry and pigs, and wild fowl, contributes to an increased risk of the emergence of novel influenza viruses in this area (10). The high standards maintained by the Hong Kong authorities in surveillance and control of avian influenza is therefore an essential part of the enhanced surveillance, which has been implemented in the region and for the global surveillance for future pandemic threats (11).