CLINICAL-FEATURES AND RAPID VIRAL DIAGNOSIS OF HUMAN-DISEASE ASSOCIATED WITH AVIAN INFLUENZA-A H5N1 VIRUS

Background Human infection with an avian influenza A virus (subtype H5 N1) was reported recently in Hong Kong. We describe the clinical prese ntation of the first 12 patients and options for rapid viral diagnosis . Methods Case notes of 12 patients with virus-culture-confirmed influ enza A H5N1 infection were analysed. The clinical presentation and ris k factors associated with severe disease were defined and the results of methods for rapid virus diagnosis were compared. Findings Patients ranged from 1 to 60 years of age. Clinical presentation was that of an influenza-like illness with evidence of pneumonia in seven patients. All seven patients older than 13 years had severe disease (four deaths ), whereas children 5 years or younger had mild symptoms with the exce ption of one who died with Reye's syndrome associated with intake of a spirin. Gastrointestinal manifestations, raised liver enzymes, renal f ailure unrelated to rhabdomyolysis, and pancytopenia were unusually pr ominent. Factors associated with severe disease included older age, de lay in hospitalisation, lower-respiratory-tract involvement, and a low total peripheral white blood cell count or lymphopenia at admission. An H5-specific reverse-transcription PCR assay (RT-PCR) was useful for rapid detection of virus directly in respiratory specimens. A commerc ially available enzyme immunoassay was more sensitive than direct immu nofluorescence for rapid viral diagnosis. Direct immunofluorescence wi th an H5-specific monoclonal antibody pool was useful for rapid exclus ion of H5-subtype infection. Interpretation Avian Influenza A H5N1 vir us causes human influenza-like illness with a high rate of complicatio ns in adults admitted to hospital. Rapid H5-subtype-specific laborator y diagnosis can be made by RT-PCR applied directly to clinical specime ns.