The symptoms of first infection are usually mild. Once recovered, immunity to that serotype of dengue virus will develop but subsequent infections with other serotypes of dengue virus are more likely to result in DHF. DHF is a severe and potentially fatal complication of dengue fever. Initially, the features include high fever, which lasts for 2 – 7 days and can be as high as 40 – 41oC, facial flush and other non-specific constitutional symptoms of dengue fever. Later, it may be followed by manifestations of bleeding tendency such as skin bruises, nose or gum bleeding, and possibly internal bleeding. In severe cases, it may progress to circulatory failure, shock and death. www.chp.gov.hk/en/content/9/24/19.html