Human Transmission of Bird Flu Media Myth
Recombinomics Commentary
February 21, 2005
>> So far, 45 people from Vietnam, Thailand and Cambodia have died from the H5N1 strain of the virus, though all but one case is believed to have been transmitted through contact with sick birds. <<
The myth listed above is perpetuated almost daily in the media, because WHO has not come out with a clear statement of human-to-human transmission on H5N1 avian influenza. Although evidence for efficient human-to-human transmission via casual contact is lacking, the evidence for human-to-human transmission from patient to care giving relative is overwhelming. The WHO has acknowledged that such transmissions are possible or probable, with the caveat that the transmission chain is short, but they have not issued a general warning on transmission of H5N1 from patient to caregiver. Proper precautions are effective. There have been no documented cases of transmission of the current H5N1 to health care workers, demonstrating that universal precautions do limit transmission. However, relatives visiting or caring for patients at home are unaware of the risks. Transmission from patient to relative is all too common and tragic, since most of the transmissions are fatal and easily avoided.
The "one case" mentioned in the myth, is the case in Thailand, which was recently published in the New England Journal of Medicine. The article did not describe an example of previously unknown H5N1 human-to-human transmission, but reported a cluster with unique circumstances that made human-to-human transmission likely. The transmission was likely because the mother of the index case did not have exposure to poultry, and the index case developed symptoms while living with her aunt, hundreds of miles away from her mother. The mother developed symptoms after visiting her daughter in the hospital. The lack of contact with fowl, coupled with development of symptoms after her daughter died, provided strong evidence for human-to-human transmission.
However, the same general features have been seen in other familial clusters, and all of these clusters had a bimodal distribution involving development of symptoms in a relative at least six days after symptoms first appeared in the index case. The bimodal distribution is strong evidence for human-to-human transmission in each individual cluster, but the bimodal distribution in ALL reported familial cases is overwhelming. Moreover, these 10 clusters involve over one third of all reported H5N1 cases in Vietnam, Thailand, and Cambodia.
The myth citing "one case" should be corrected by a strong warning from the WHO on transmission of H5N1 from patients to caregivers who do not adhere to universal precautions.
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