Update: WHO-confirmed human cases of avian influenza A(H5N1) infection, 25 November 2003–24 November 2006

It is 3 years since WHO began recording human cases of infection with avian influenza A(H5N1). A description of 205 laboratory-confirmed cases occurring up to 30 April 2006 found that 90% of cases were in people aged <40 years, that the overall case-fatality rate was 56%, that the median interval from illness onset to hospitalization was 4 days, and that the median duration from illness onset to death was 9 days. This article is a brief follow-up summary of that initial epidemiological description. A total of 51 additional human cases of H5N1 have been confirmed since that time; outbreaks in birds continue to be reported worldwide.