A deadly form of "bird 'flu'", the H7N9 Avian Influenza A virus, was detected in four provinces of eastern China, where it has infected 135 people, and 44 of the infected individuals have died in the course of the past five months. These incidents are of particular importance, since it is the first time that this subtype of the Avian Influenza A virus has been verifiably transmitted from infected poultry to humans. The public health risk remains low at present. No cases of poultry or human infection from this novel H7N9 subtype have yet been reported outside China. The virus is classified as "low pathogenic", which means that the infected birds appear healthy although they carry the H7N9 virus and are thus a potential threat to human health.