Serological and virological features of dengue fever and dengue haemorrhagic fever in Thailand from 1999 to 2002.

Serological and virological features of dengue fever (DF) and dengue haemorrhagic fever (DHF) in Thailand were analysed in 2715 patients from 1999 to 2002. The illness was caused by DEN-1 in 45%, DEN-2 in 32%, DEN-3 in 18% and DEN-4 in 5% of patients. Almost all of the DHF cases caused by DEN-2 and DEN-4 were in secondary infection, while approximately 20% of the DHF cases caused by DEN-1 and DEN-3 were in primary infection. Male:female ratio and age distribution were not different among four serotypes in primary and secondary infections. These results indicate that DEN-1 and DEN-3 induce DHF in both primary and secondary infections, and suggest that DEN-2 and DEN-4 in Thailand are less likely to cause DHF in primary infections.