The World Health Organisation has released a report analysing the epidemiology all 205 confirmed cases of human bird flu infections.
The report, although based on somewhat inconsistent global data, draws several conclusions about avian influenza:
– The number of new countries reporting human cases increased from 4 to 9 after October 2005, following the geographical extension of outbreaks among avian populations.
– Half of the cases occurred in people under the age of 20 years; 90% of cases occurred in people under the age of 40 years.
– The overall case-fatality rate was 56%. Case fatality was high in all age groups but was highest in persons aged 10 to 39 years.
– The case-fatality profile by age group differs from that seen in seasonal influenza, where mortality is highest in the elderly.
– The overall case-fatality rate was highest in 2004 (73%), followed by 63% to date in 2006, and 43% in 2005.
– Assessment of mortality rates and the time intervals between symptom onset and hospitalization and between symptom onset and death suggests that the illness pattern has not changed substantially during the three years.
– Cases have occurred all year round. However, the incidence of human cases peaked, in each of the three years in which cases have occurred, during the period roughly corresponding to winter and spring in the northern hemisphere. If this pattern continues, an upsurge in cases could be anticipated starting in late 2006 or early 2007.
For more information, view the full Epidemiology of WHO-confirmed human cases of avian A(H5N1) infection report.