OBJECTIVETo ascertain the causation of a family cluster involving two undefined pneumonia cases, a 12-year-old girl and her brother, reported October, 2005 in Xiangtan county, Hunan province.

METHODSInformation on epidemiology and clinical manifestation of the cases was collected from interviewing the keyman and referring to related medical records. The environment exposure of the cases to their households and the timeline of the illness were reproduced, using this information. Medical check-up was undergone among the close contacts of the cases and on sick/dead poultry. Throat swab of the cases were collected and tested by both RT-PCR and real-time PCR to detect viral nucleic acids of A/H5N1, and were then inoculated into special pathogen free (SPF) embryonated hens' eggs. Serum of the cases including acute and convalescent phases were also collected and tested by microneutralization and haemagglutination-inhibition (HI) assays to detect H5-specific antibodies.

RESULTSBoth the girl and her brother developed fever 2 and 4 days after sudden deaths of chickens being raised in the same house. Both of them had developed pneumonia and the girl died from acute respiratory distress syndrome (ARDS) complicated with multi-organ failure. The boy survived and subsequently discharged from hospital. An eighth-day serum from the girl tested H5 antibody negative, while 4-fold and greater increased in antibody titers were detected in serum from the boy using microneutralization and HI assays in sequential acute and convalescent sera. Of 192 cases, only one doctor who cared for the girl during hospitalization had upper respiratory symptoms but tested negative for H5N1 by microneutralization assay.

CONCLUSIONThe boy was the first confirmed human case of avian influenza A (H5N1) in the mainland of China and his sister was diagnosed clinically. The most probable explanation of these two cases was that the transmission of H5N1 virus from infected poultry within the same household environment. No evidence of human-to-human transmission was noted in the family cluster.