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Dong Thap Familial Bird Flu Cluster Details
January 29, 2005
The six-day interval between the Vietnamese mother and child developing symptoms means that human-to-human transmission can't be ruled out, the WHO said of the latest case.
``If they'd both developed symptoms on the same day, it would mean it's very unlikely that the mother passed the disease on to the child,'' said Peter Horby, an epidemiologist with the WHO in Hanoi………
All such clusters of cases that are closely related in time and place require urgent investigation to determine whether the virus's behavior may be changing in ways that may favor the beginning of a pandemic, the WHO said.. ..
``This avian virus seems to have the ability for limited human-to-human transmission, so we are not surprised to see family clusters,'' said Horby. ``But these cases must be investigated fully to make sure there's no further transmission.''
The details of the family clusters are important. The disease onset dates take on added importance as the number of potential poultry sources increase along with the number of locations with multiple confirmed or suspected cases. This mother-daughter familial cluster is a good example of a large number of potential poultry sources as well as human sources.
Media reports on potential sources of infection for the mother include a canal that she bathed in, a body of water that she swam in, stork droppings near a pond near her work, a duck that she slaughtered (with no infection of family members who ate the duck), and a duck that she slaughtered with her daughter, who is also a confirmed fatality.
Media reports cite the duck slaughter as a source of infection for the daughter, but the six day onset differential raises doubt on a common source for mother and daughter.
Paralleling the large number of poultry sources for the mother's infection is a large number of human sources. The Dong Thap cluster of geographically linked cases is large. Most media reports of confirmed or suspect cases already have advanced disease, including lung involvement. Many are already critical and on ventilators. There are likely additional cases at earlier stages in the disease progression.
Media reports on cases linked to Dong Thap include this seasons first confirmed case (16F) who brought a chicken from Dong Thap to her uncle, as well as the second confirmed H5N1 avian influenza fatality (6M) this season. Both of these cases showed symptoms in December. They could be linked to other human sources. There was no reported contact with sick birds for the boy.