Antibody response in individuals infected with avian influenza A (H5N1) viruses and detection of anti-H5 antibody among household and social contacts

The first documented outbreak of human respiratory disease caused by avian influenza A (H5N1) viruses occurred in Hong Kong in 1997, The kinetics of t he antibody response to the avian virus in H5N1-infected persons was simila r to that of a primary response to human influenza A viruses; serum neutral izing antibody was detected, in general, greater than or equal to 14 days a fter symptom onset. Cohort studies were conducted to assess the risk of hum an-to-human transmission of the virus. By use of a combination of serologic assays, 6 of 51 household contacts, 1 of 26 tour group members, and none o f 47 coworkers exposed to H5N1-infected persons were positive for H5 antibo dy. One H5 antibody-positive household contact, with no history of poultry exposure, provided evidence that human-to-human transmission of the avian v irus may have occurred through close physical contact with H5N1-infected pa tients. In contrast, social exposure to case patients was not associated wi th H5N1 infection.