[Epidemiology of dengue fever in Taiwan]

Dengue fever, a tropical communicable disease, is caused by an infectious viral disease. It is also known as break bone fever. There have been a number of epidemics over the last century in Taiwan. Following an islandwide epidemic in 1942, dengue fever had not been presented on the island for about forty years. In 1981, an outbreak of dengue occurred in Liuchiu Hsiang, a small off-shore island of Pingtung county. The estimated attack rate was 80%. DEN-2 was isolated during that outbreak. Another occurrence occurred in the fall of 1987 in the southern part of Taiwan. The accumulated reported cases reached 1,387 at the end of that year. A majority of cases were reported in the Sanmin district of Kaohsiung city. The reported cumulative incidence was 0.2% in Sanmin. However, according to one survey, the attack rate in that area was 2.9%. DEN-1 was most commonly isolated but DEN-2 was also found in five cases. The latest outbreak took place in 1988. The estimation of reported cases exceeded 10,000 at the end of November, 1988. Two cases of dengue haemorrhagic fever were confirmed. More than fifty percent of the report case came from Kaohsiung city. The reported cumulative incidence rate was 0.5% in that area. Another survey reported that the adult attack rate exceeded 5% in the same area. It is estimated that the number of patients with mild symptoms and those without any symptoms would be a few times more than the number of those actually reported. However, a large space of herd immunity for susceptible hosts has remained. DEN-1 was isolated from all of the reported cases except two in which DEN-4 were isolated. Among the various variables which would effect the proliferation of disease, such as Aedes aegypti density, precipitation, and temperature, only a prior month of precipitation can explain the outbreak of dengue by stepwise multiple regression. Besides this, there was also a higher relative risk due to a higher population density with a trend correlation. Because of the ineffectiveness of the present control program, it is predicted that there may be yet another outbreak in the following year effecting those susceptible when the rainfall season comes.