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Proven Human to Human H5N1 Transmission in China
December 21, 2007
The World Health Organization said Friday it was impossible to say whether a case of bird flu in China involving a 52- year-old man was due to human-to-human transmission - but, even if it was, it was down to very close contact between the victims.
The Assistant Director-General for Health Security at WHO, Dr David Heymann, said the only proven transmission of this nature so far, in Indonesia and Thailand, had been as a result of very "close contact" in a "very circumscribed area."
The above comments are yet another extension of the media myth on human to human transmission of H5N1. In the cluster in Jiangsu, China, the father developed symptoms just as his son was buried 8 days after disease onset. This time gap is typical for human to human transmission, and is common for H5N1 familial clusters.
However, the obvious cases are followed up by an epidemiological “investigation”, which has no scientific basis, but generates the equivalent of an “internet rumor” to explain the transmission. In this case, the two victims were said to be infected by consumption of a chicken at a restaurant. There was no epidemiological evidence to support this source. No one at the restaurant developed bird flu symptoms and no one else who ate the dish developed symptoms. Moreover, the two victims developed symptoms 8 days apart. Victims usually develop symptoms 2-4 days after exposure, so if both victims were exposed to a common source, they would be expected to develop symptoms at the same time.
The story was embellished further with speculation that the index case developed symptoms early (one day after the meal), because he had been receiving rabies shots due to an earlier dog bite. The lack of transmission to other family members, who at the same dish, was postulated to be due to differences in the cooking of white and dark meat. This yarn was then posted on ProMed, a newsletter that is supposed to present scientific data on infectious disease. It is widely read by media, and the general public, leading to “viral” spread of the yarn via the internet.
Unfortunately, these ad hoc non-scientific explanations have been used repeatedly by WHO to explain away obvious human to human transmission, so they can issue statements such as the one quoted above.
In 2005, blaming duck blood pudding was the fashionable to explain away human to human H5N1 transmission. One cluster was almost exactly three years ago in northern Vietnam. The index case developed symptoms a day after slaughtering a duck for a holiday dinner. His brother developed symptoms 17 days after the dinner, which included duck blood pudding. A brother-in-law who also ate the duck blood pudding did not develop symptoms, while a third brother who didn’t eat the blood pudding did develop H5N1 antibodies. Thus, once again there was no evidence that the duck blood pudding had anything to do with the cluster, but WHO not only used the yarn to explain the cluster, but then modified its description of H5N1 infections to state that incubation periods could be as long as 17 days!
The duck blood pudding story was used again two months later to explain away another cluster. The index case developed symptoms five days after eating duck blood pudding at a friend’s house as part of the celebration of the Tet New Year. His sister developed symptoms 10 days after the meal. Another sister who had the meal did not develop symptoms, but the grandfather who didn’t eat the dish developed antibodies. Moreover, a nurse who had contact with the index case was H5N1 positive, and another nurse developed symptoms but tested negative. Once again there was no evidence that the blood pudding had anything to do with the infection. The two victims developed symptoms too late, another relative who had the dish didn’t develop symptoms or antibodies, while another relative who didn’t have the dish did. Similarly, no one at the friend’s house developed symptoms or antibodies. The sister who did get infected was infected why on prophylactic Tamiflu, which led to a Tamiflu resistant strain emerging ion samples from the sister. Eventually all recovered, but the siblings and nurse were H5N1 lab confirmed.
The best data point for distinguishing infection from a common source from human to human transmission is the time gap between the disease onset dates. If there is a gap, it is highly likely that the gap is due to incubation times associated with human top human transmission. In most cases, there will be a common source available, because many times the index case is infected by a poultry source, so other family members are in the general region of the source. However, transmission from a poultry source is rare. However, when a family member brings the H5N1 inside the home or the vehicle used to transport the victim, the close contact can lead to H5N1 transmission.
The gap in disease onset dates in H5N1 clusters is obvious, as is the efforts to spin yarns to discount the obvious human to human transmission.
Recombinomics Paper at Nature Precedings