Where and how many human cases have occurred?
Hong Kong experienced the first H5N1 virus outbreak in humans in 1997 with 18 cases and six deaths.
In early 2003, the virus caused two infections and one death in a family in Hong Kong who had recently traveled to southern China.
There had been no cases in humans elsewhere in the world until that time.
Since 2003, the outbreak has resulted in 121 laboratory-confirmed human cases with 62 deaths reported in four countries: Cambodia, Indonesia, Thailand and Viet Nam.