Source:  Classification    Tag:  dengue virus classification
The World Health Organization's 2009 classification divides dengue fever into two groups: uncomplicated and severe.[1][23] This replaces the 1997 WHO classification, which needed to be simplified as it had been found to be too restrictive, though the older classification is still widely used.[23] The 1997 classification divided dengue into undifferentiated fever, dengue fever, and dengue hemorrhagic fever.[5][24] Dengue hemorrhagic fever was subdivided further into grades I–IV. Grade I is the presence only of easy bruising or a positive tourniquet test in someone with fever, grade II is the presence of spontaneous bleeding into the skin and elsewhere, grade III is the clinical evidence of shock, and grade IV is shock so severe that blood pressure and pulse cannot be detected.[24] Grades III and IV are referred to as "dengue shock syndrome.