Influenza A(H9N2) infections in Hong Kong

In March 1999, the Hong Kong Department of Health (HKDH) isolated influenza A viruses from two children (1 and 4 years of age) that could not be further identified using the usual influenza reagents. The viruses isolated from the children were sent to the National Institute for Medical Research, London and CDC, Atlanta. In April 1999, both laboratories identified the viruses as influenza A(H9N2). These are the first confirmed human infections with influenza A(H9N2) viruses. Five additional cases were reported from mainland China but have not been confirmed. No additional confirmed or suspected human cases of A(H9N2) infection have been identified in Hong Kong, thus far, and surveillance in Hong Kong has not shown evidence of increased respiratory illness activity. The influenza A(H9N2) virus is different than the influenza A(H5N1) viruses which caused an outbreak of influenza (the "Avian Flu") in Hong Kong in 1997.

Influenza A(H9N2) is an avian flu virus and usually infects birds. However, influenza A(H9N2) does not appear to cause high rates of death in poultry as did influenza A(H5N1) in Hong Kong. It is not known how the 2 children in Hong Kong became exposed to influenza A(H9N2). Both children were hospitalized but recovered fully.

Studies are being conducted by the HKDH, in collaboration with other international groups, including the World Health Organization and CDC, to assess the public health implications of this finding.

There are no warnings or precautions for travel to Hong Kong at this time.

In the United States, the 1999-2000 flu vaccine will consist of A/Sydney/5/97-like (H3N2) strain, A/Beijing/262/95-like (H1N1) and B/Yamanashi/166/98 strain. An A(H9N2) virus will not be added to the 1999-2000 vaccine. However, similar to the A(H5N1) outbreak, discussion and preliminary work will begin on developing a candidate vaccine for the new flu virus.

For more information out the influenza A(H9N2) outbreak in Hong Kong, visit this website http://www.info.gov.hk/eindex.htm

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U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES