Discussion
A key assumption of this study was that HPAI H5N1 is endemic in Purbalingga District. The concept of endemicity assumes firstly that the virus is permanently present. H5 virus was detected throughout the period of active sampling, and in all enterprise types (albeit at very low levels in backyard and commercial poultry). Therefore, we conclude that H5N1 HPAI may be assumed to be endemic in Purbalingga District, and that all poultry enterprise types have at least the potential to contribute to HPAI spread and persistence. Extrapolating this, if the conditions in Purbalingga District can be considered representative of a wider area (e.g. Java), it is likely that H5N1 HPAI is endemic in this wider area (although it may not be endemic in all areas, all year round).