Background In May, 1997, a 3-year-old boy in Hong Kong was admitted to
the hospital and subsequently died from influenza pneumonia, acute re
spiratory distress syndrome, Reye's syndrome, multiorgan failure, and
disseminated intravascular coagulation. An influenza A H5N1 virus was
isolated from a tracheal aspirate of the boy. Preceding this incident,
avian influenza outbreaks of high mortality were reported from three
chicken farms in Hong Kong, and the virus involved was also found to b
e of the H5 subtype. Methods We carried out an antigenic and molecular
comparison of the influenza A H5N1 virus isolated from the boy with o
ne of the viruses isolated from outbreaks of avian influenza by haemag
glutination-inhibition and neuraminidase-inhibition assays and nucleot
ide sequence analysis. Findings Differences were observed in the antig
enic reactivities of the viruses by the haemagglutination-inhibition a
ssay, However, nucleotide sequence analysis of all gene segments revea
led that the human virus A/Hong Kong/156/97 was genetically closely re
lated to the avian A/chicken/Hong Kong/258/97. Interpretation Although
direct contact between the sick child and affected chickens has not b
een established, our results suggest transmission of the virus from in
fected chickens to the child without intermediate mammalian host as a
acting vessel''. This event illustrates the intensive global influenza
surveillance.