24.02.2012

Wang et al (2012) Science

WHO documented cases of avian H5N1 influenza infections in humans reported from 15 countries. Of the WHO confirmed cases, 58.6% have resulted in death (as of December 15th, 2011). These severe H5N1 infections were diagnosed using criteria developed by the WHO that are specific for H5N1 disease, but that lack the sensitivity to identify the total number of human infections. Given the fact that most H5N1 infections in poultry and in humans occur in resource-poor areas where access to health care is often arduous and expensive to obtain, Wang et al (2012) hypothesized that many people with H5N1 virus infection would not have been examined by a health provider to allow formal H5N1 disease confirmation. In addition, persons who are seropositive for H5N1 infection often report no history of influenza-like illness, and subclinical or mild H5N1 infections are not recognized under the WHO criteria for confirmed cases. The researchers conducted a meta-analysis of studies that evaluated the serological evidence of H5N1 infections in humans.
Although it is not possible to determine an accurate fatality rate for H5N1 infections based on the data presented in the study, if one assumes a 1-2% infection rate in exposed populations, this would likely translate into millions of people who have been infected, worldwide.