Commentary
More Media Myth on H7 Transmission
Recombinomics Commentary 20:04
June 4, 2008
The most publicised case was recorded in the Netherlands during an extensive epizootic of HPAI H7N7 virus on commercial poultry farms, between March and May 2003. One case involved fatal respiratory distress syndrome in a veterinarian who was in close contact with infected poultry -- see ProMED ref. below. Reportedly, 86 cases in poultry workers and 3 cases in people with no poultry contact were initially confirmed by PCR.
The majority of H7 infections have resulted in self-limiting conjunctivitis, whereas probable human-to-human transmission has been rare.
The above ProMED comments are internally inconsistent. The first paragraph acknowledges the 89 PCR confirmed H7 human cases from the 2003 H7N7 outbreak in The Netherlands, including three cases with no direct link to poultry, and then claims that probable human-to-human transmission has been rare. The difference between H7 transmission to humans from humans or poultry is slight. The 89 confirmed cases indicate transmission of H7 to humans is common, and the three cases confirmed above would move the H2H transmissions from the “rare” category.
The 89 cases from a single outbreak are more than H5N1 cases in any country in any year, and only Vietnam and Indonesia have had more H5N1 infections over multiple years. H7 transmission to humans is much more common than H5N1, even though the sensitivity of H7 assays is exceedingly low.
The case for probable H2H transmission was significantly increased by follow-up studies on H7 antibodies in the above cases and contacts. Over 1000 cases were identified and 59% of culler contacts were positive, indicating the sensitivity of the PCR testing was very low and H2H transmission was very common.
The efficient H7 transmission was also supported by the H7N3 outbreak in British Columbia the following year. Fifty seven cases associated with the outbreak had suspected avian influenza, but only two were confirmed. Media reports indicated that many of the cullers had conjunctivitis, suggesting that most or all of the “suspect” cases had similar symptoms, and the low number of confirmed cases indicates they either tested negative or were not tested at all. 55 cases from a single outbreak would again signal efficient transmission to humans, which would again support H2H.
The same type of result was reported a year ago in England in the H7N2 low path outbreak. Although only four were confirmed, one of the four had no direct contact with poultry, and many of the negative patients had symptoms at a time when seasonal flu in England was minimal.
The human cases in the above H7 outbreaks involving three different serotypes and both high and low path avian influenza supports common transmission to and transmission between humans.
The data do not support the above Pro-MED statement or statements issued by DEFRA on transmission to humans. The mis-statements are used by the popular press to spread the misinformation, creating or extending a media myth, which continues to be hazardous to the world’s health.
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