Most cases of dengue fever are self-limited in their course and never progress to dengue hemorrhagic fever. So what are the factors associated with the occurrence of DHF?

• Virus strain: DHF can occur in primary infection with certain genetic strains of virus.
• Pre-existing anti-dengue antibody, either caused by previous infection or to maternal antibodies passed to infants.
• Host genetics—for example, race seems to be a factor: data from Cuba suggest that whites may be at greater risk, and blacks at lower risk. And
• Age—in Southeast Asia, children are most affected, though in the Americas, all age- groups are affected.