December 27, 1997
Antibody to influenza A H5N1 virus was found in nine blood samples out of 502 tested in relation to the first avian flu case detected in Hong Kong. The antibody to the virus was detected mainly among poultry workers and people directly exposed to the virus.
The results, based on studies related to the first avian flu case in a human, suggested that the main mode of H5N1 transmission was from bird-to-human. Analysis of the viral genes shows that they are avian in nature without evidence of re-assortment with human influenza virus genes.
The results leave open the possibility of person-to-person transmission. However, the absence of antibody among the family members of the ill child and the overall low number of antibody positive people in contact with the child suggested that such transmission, if occurring, is relatively inefficient at this time.
These preliminary results and findings were released today (Saturday) jointly by the Hong Kong Department of Health, WHO and the Centers for Disease Control (CDC) and Prevention in Atlanta, USA. They stressed that the observations were preliminary and were based on serological test results done in connection with the first patient, using a microneutralization assay developed at CDC.
Additional findings are expected by late January next year when test results of other cases become available and other studies currently being conducted are completed.
The nine persons tested positive of antibody were all from the 502 people in the "exposed group", made up of poultry workers, people in contact with the boy and people working with the virus, such as laboratory workers.
In contrast, another 419 people in a "comparison group" who had no history of contact with the ill child were all negative for influenza A H5N1 antibody.
These results suggested that poultry workers and people known to have had direct contact with the virus were more likely to have antibody to this virus.
The nine antibody positive persons out of the 502 tested (1.8 per cent) were from the following groups:
People potentially in contact with the child
People in the same district
Laboratory workers
People exposed to poultry or pigs
Follow up investigation of the nine antibody positive persons indicated that five were poultry workers, one was a student with exposure to poultry, one was a laboratory worker and one was a person whose exposure history was not clear.
The remaining antibody positive person was a healthcare worker who helped take care of the child. The healthcare worker gave no history of exposure to poultry raising the possibility of human-to-human transmission.
These data are consistent with the possibility that influenza A H5N1 virus might be transmitted to humans by:-
"The Hong Kong Government has already initiated measures to help make sure that chicken sold in the market are free of avian flu," the Director of Health, Dr Margaret Chan said.
"With the co-operation of the mainland authority, export of chicken from the mainland to Hong Kong has been temporarily suspended to allow time to put in place a system in the mainland to ensure the health status of chicken exported to Hong Kong and a system here to conduct rapid tests on chicken imported again in the future."
"So far, surveillance of local farms has not detected any chicken that are positive for influenza A H5N1. The situation will be closely monitored by the Agriculture and Fisheries Department."
"At the wholesale and retail levels, blitz cleaning of chicken stalls has been started and will continue over the next few days to improve the hygiene conditions of these places."
"All these public health measures are taken to ensure that chicken sold in Hong Kong are healthy and to rebuild consumers' confidence."