The consensus among many scientists has been that the strain of bird flu currently circulating – H5N1 – is not only highly infectious, but potentially deadly. That is based on the nearly 600 cases confirmed by the World Health Organization, more than half of which have resulted in death.
But a new study analyzing WHO data suggests that H5N1 may not be as virulent as previously thought, and that mild infections could be slipping under the radar because of less-than-ideal detection methods.
Were those mild cases included, the death rate due to H5N1 could be dramatically lower, according to research appearing in the journal, Science.
"People who have evidence in their blood of prior H5N1 infection often report no history of flu-like illness," said Taia Wang, a study co-author and scientist at the Mount Sinai School of Medicine Department of Microbiology, in an email to CNN. "These cases are not identified using current WHO criteria but they are true infections and should be taken into account when calculating a fatality rate associated with H5N1 viruses."
According to Wang, strictly-defined parameters must be met to confirm an H5N1 case: a high fever, verifiable exposure to the H5N1 virus within seven days of diagnosis, and confirmation of infection by a WHO-approved laboratory.
"These criteria were designed to be extremely specific for identification of H5N1 disease, but they are not sensitive enough to identify less severe cases," said Wang.
H5N1 is lethal to certain species of birds, and in its present form, rarely infects humans. But WHO data suggest that when H5N1 does jump to humans, the potential for death is high. Of 586 people infected by H5N1 thus far, according to WHO data, 346 died.
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