00000000The first case of DHF was reported in the South in 1963 and in the North in 1969. DHF has since become a major public health problem with the annual number of cases being the highest in the Western Pacific region. From 1975 to 1983 epidemics occurred almost annually, and the incidence varied from 52.3 to 260.6 per 990 000 population(14). Severe epidemics occurred in the whole country in 1975, 1977, 1978, 1979, 1980 and 1983. The most severe epidemic occurred in 1983 in all parts of Viet Nam, and 149 519 cases with 1798 deaths (case fatality rate of 1.2 per cent) were reported. In South Viet Nam, most of the DHF cases were children in the five to six year age group whereas in the North adults were also involved(14). There appeared to be equal numbers of male and female cases.

00000000It has also been observed that epidemics of DHF occur mainly in the rainy season, the breeding period of A. aegypti. All four serotypes of dengue virus have been isolated from human cases of DHF as well as from A. aegypti mosquitoes(14). There have also been claims that dengue-1 (DEN-1) and DEN-2 viruses have been isolated from Culex fatigans(14). The positivity of paired sera sent for serological confirmation by the HI test ranged from 34.3 per cent to 55.4 per cent.

00000000A summary of DHF activity in Viet Nam from 1975 to 1983 is given in Table 2.

Table 2. Dengue Haemorrhagic Fever (DHF) in Viet Nam, 1975 - 1983*

* Source of data: (14), (15)