Epidemiology of Dengue in Singapore - Current situation

Abstract

There has been a resurgence of dengue fever/dengue haemorrhagic fever (DF/DHF) cases in Singapore in recent years. Following the large outbreak in 1973 with 1,187 cases and 27 deaths, the incidence of DF/DHF declined with minor bi-annual outbreaks occurring in 1978, 1980 and 1982. Beginning from 1986, however, the DF/DHF situation changed for the worse when outbreaks of increasing size occurred almost annually. In the past 3 years, there were 1,733 cases in 1990, 2,179 cases in 1991 and 2,878 cases in 1992. In the 1991 and 1992 outbreaks, 93-95% of the notified cases required hospitalization and 92-95% of them were serologically confirmed by the IgM capture ELISA and/or the commercial Dengue Blot assay. The number of fatal cases, however, remained low with 3-6 reported deaths in the three outbreaks. All age groups were affected with the highest morbidity rate in children and young adults between 15 and 24 years of age. In contrast, in the earlier 1973 and 1978 outbreaks, more patients below the age of 15 years were observed. There was a slight predominance among males and Chinese had the highest morbidity rate compared with Malays and Indians. The recent outbreaks occurred mainly in highly populated urban and suburban areas in the eastern, northeastern and southeastern parts of the island. Patients living in landed property such as compound houses had a 9 x higher morbidity rate than those living in high-rise flats. Cases were reported throughout the year and the number increased during May and June. The increased DF/DHF incidence was preceded by an increase in the Aedes mosquito population. In the 1991 and 1992 outbreaks, although the overall Aedes house index was <1 for both Ae aegypti and Ae albopictus higher indices were detected in localized areas with high dengue transmission. The proportion of compound houses found breeding Ae aegypti was 3-4 times and Ae albopictus 7-10 times higher than that of flats. The major breeding habitats were ornamental and domestic containers and discarded receptacles.