The United Nations World Health Organization (WHO) is helping authorities in Thailand determine if two recent cases of bird flu are evidence of the first human-to-human transmission of the virus, raising fears of a possible influenza pandemic.
Since yesterday the Thai Ministry of Public Health has confirmed two new cases of H5N1 avian influenza in humans: a 26-year-old woman who died on 20 September and her 32-year-old sister, who remains hospitalized in stable condition, WHO said.
While the investigation of this family cluster provides clues that human-to-human transmission may have occurred, evidence so far indicates that spread of the virus among humans has been confined to family members, the agency added.
Dr. Klaus Stöhr, Coordinator of WHO's Global Influenza Programme, said the incident could be a "non-sustained, inefficient, dead-end street human-to-human transmission."
But he warned that it also could also indicate the beginning of more widespread, sustained transmission "which could lead to the global spread of this virus, and that's what we would fear, namely that such a virus would acquire the human-to-human transmissibility."
Thai officials suspect the first woman's 11-year-old daughter - who died of pneumonia on 8 September - was the initial case, although laboratory confirmation is not possible as no specimens from this patient are available for testing. The 6-year-old son of the woman's sister was hospitalized but is recovering, and samples from him are being tested.
The girl, who lived in the northern province of Kamphaeng Phet, resided with her aunt, whose infection has been confirmed. Both patients are known to have had contact with dead chickens.
The girl's 26-year-old mother, whose infection is also now confirmed, resided in the Bangkok area, but provided bedside care for her daughter while she was hospitalized, up to the time of the child's death. The mother fell ill upon her return to Bangkok, where she died on 20 September.
Thai officials have concluded that the mother could have acquired the infection either from some environmental source or while caring for her daughter, and that this represented a probable case of human-to-human transmission, WHO said.
Clinical samples taken from cases in the family cluster were immediately shared with a laboratory in the WHO Global Influenza Surveillance Network. Virus isolated from these samples will undergo genetic and antigenic analysis to determine whether the virus has evolved and, more specifically, whether it has acquired genes that allow improved transmissibility among humans.
The new cases bring to three the total in Thailand confirmed since early September. Altogether, the country has reported 15 cases, of which 10 were fatal, since the first human cases were detected in January of this year.