H5N1 Bird Flu Infection May Be More Common, Less Deadly, Than Thought
The World Health Organization says the H5N1 bird flu kills nearly 60% of people who become infected, but a study released Thursday suggests the true fatality rate may actually be much lower.
Virologists at the Mount Sinai School of Medicine in New York City examined data on blood samples collected from more than 12,000 people in Asia, Europe and Africa and found evidence of H5N1 infection in 1% to 2% of cases. Most of those people did not become ill with the flu, according to a report in the journal Science, and none of them died.
The findings, which used data from 20 previously published studies, suggest that many more people have been infected with H5N1 flu viruses than the 586 officially confirmed by the WHO as of Wednesday; if so, the fatality rate could be lower than the 59% reported by the global health agency.
“The World Health Organization criteria that are currently being used for confirmation of H5N1 infections are good for the identification of very severe cases, but they do not pick up the cases that are mild or asymptomatic” because such patients are less likely to seek treatment in a hospital, said postdoctoral researcher Taia Wang, who led the study.
Flu experts have speculated before that the WHO’s surveillance system is patchy and misses an unknown number of cases. There is no scientific consensus about what the true fatality rate is.
Gregory Hartl, a WHO spokesman in Geneva, acknowledged Thursday that the agency’s criteria for confirming bird flu cases might underreport mild cases. But he said it was more likely that officials were missing cases of bird flu deaths