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3 Generations of Human Transmission of Bird Flu in Vietnam?
January 22, 2005
>> A 45-year-old man from Thai Binh province died on January 9 in Hanoi. One of his brothers, has also tested positive for the virus. The 42-year-old is in a stable condition in a Hanoi hospital.
Another brother, aged 36, was also in hospital with a suspected infection.
According to several sources, all three had shared a meal of duck meat and blood pudding in their homeland province of Thai Binh, southeast of the capital, in late December.
Blood pudding, made mostly from ducks and pigs, is a favourite dish among many Vietnamese but authorities have urged people to avoid it to prevent the spread of bird flu.
If confirmed, this form of contamination would clear earlier fears that human-to-human transmission had occurred among the brothers.<<
There really is no way to "confirm" one hypothesis over the other. Infection of all three brothers from a common source, or three generations of transmission would each generate the same virus in all the patients.
The two hypotheses would be distinguished by dates of onset of symptoms, which clearly favor 3 generations of human to human transmission. The meal was last year and the index case (45M) developed symptoms on Jan 1 and died Jan 9. One of his brothers (42M) developed symptoms on Jan 10 after caring for his older brother. The development of symptoms 9 days after his older brother provides strong evidence for human to human transmission, characterized as "likely" by Klaus Stohr, from WHO.
The third brother (36M) was admitted to the hospital on Jan 20, 10 days after symptoms in one brother (42M) and 19 days after symptoms in the index case (45M) and well over 3 weeks after the meal described above. The disease onset dates clearly favor a three generation transmission of avian influenza, which would be a longer chain than the two earlier clusters in Thailand and Vietnam.
The longer chain of transmission, coupled with the difficulty in generating H5N1 confirmation in several instances are causes for concern.