Southeast Asian hemorrhagic fever: A syndrome due to the dengue virus that tends to affect children under 10, causing abdominal pain, hemorrhage (bleeding) and circulatory collapse (shock). Known also as dengue hemorrhagic fever (DHF), it starts abruptly with high continuous fever and headache plus respiratory and intestinal symptoms with sore throat, cough, nausea, vomiting, and abdominal pain. Shock occurs after 2 to 6 days with sudden collapse, cool clammy extremities, weak thready pulse, and blueness around the mouth (circumoral cyanosis). There is bleeding with easy bruising, blood spots in the skin (petechiae), spitting up blood (hematemesis), blood in the stool (melena), bleeding gums and nosebleeds (epistaxis). Pneumonia and heart inflammation (myocarditis) may be present. The mortality is appreciable ranging from 6 to 30%. Most deaths occur in children. Infants under a year of age are especially at risk of death. It is also called Philippine or Thai hemorrhagic fever and dengue shock syndrome.