Risk Factors
DHF is rarely seen in persons older than 15 years of age. Other risk factors for development of DHF include having a history of dengue infection; the presence of antibodies to a different dengue serotype is thought to enhance viral replication, increasing the severity of the disease. Susceptibility to DHF may vary by race; although all four dengue serotypes are seen in Africa, DHF is very rare. Studies have suggested that certain HLA alleles may confer protection against DHF, while others seem to increase the risk.