Dengue 1 Virus and Dengue Hemorrhagic Fever, French Polynesia, 2001

An epidemic of dengue 1 virus (DENV-1) occurred in French Polynesia in 2001, 4 years after a DENV-2 epidemic that ended in 1997. Surveillance data from hospitalized case-patients showed that case-patients with dengue hemorrhagic fever (DHF) exhibited a bimodal age distribution with 1 peak among infants 6-10 months of age and a second peak at 4-11 years of age. The relative risk of DHF developing in children born before rather than after the DENV-2 epidemic was 186 (95% confidence interval 26-1,324). Among children born toward the end of the DENV-2 epidemic, a strong temporal association was found between the month of birth and the risk of being hospitalized for DHF. This study documents epidemic pathogenicity associated with the sequence of DENV-2 infection followed by DENV-1 infection.