Bird flu. Conceptual artwork of a chicken and flying syringes, representing measures taken against the spread of avian influenza (bird flu). The background figures indicate this is the H5N1 variant of the influenza A virus. Although this form does not typically infect humans, in 1997, the first instance of direct bird-to-human transmission was identified during an outbreak of avian influenza in Hong Kong poultry. It caused severe respiratory illness in 18 people, six of whom died.