Epidemic dengue transmission in southern Sumatra, Indonesia

An outbreak of dengue fever (DF), dengue haemorrhagic fever (DHF), and deng ue shock syndrome (DSS) in the city of Palembang, south Sumatra, Indonesia was investigated to (i) validate epidemic occurrence, (ii) confirm dengue v irus aetiology and associated serotype(s), (iii) provide a demonstrable mea sure of community impact, and (iv) identify causative relationship (if any) with climatic El Nino Southern Oscillation (ENSO) influences. Trend analys is based on a 6-year retrospective review of hospital records demonstrates a 3-fold increase in clinical cases for the outbreak period (January-April 1998), relative to historical records. In the 2 hospitals surveyed, the mon thly mean number of outbreak-related dengue cases over 4 months was 833 (ra nge 650-995 cases/month); the mean monthly value for the previous 72 months was 107 (range 14-779 cases/month). An apparent trend in epidemic transmis sion was observed, evolving from a 5-year cyclic phenomenon to an annual oc currence, often indistinguishable from one year to the next. The proportion al distribution of clinical outbreak cases into DF, DHF and DSS diagnostic categories was 24%, 66%, and 10%, respectively. The population aged 10-19 y ears accounted for the largest (35%) proportion of hospitalized DHF cases, followed by children aged 5-9 years (25%) and children aged 4 years (16%). Serum samples obtained during acute illness from 221 hospitalized patients were examined using serology, RT-PCR, and virus isolation in cell culture: 59% of samples had laboratory evidence of a dengue infection. All 4 dengue virus serotypes (DEN 1-4) were identified in epidemic circulation, with DEN 3 predominating (43%). DEN 1 was the principal serotype associated with le ss severe dengue illness, suggesting that virulence may be, in part, a func tion of infecting serotype. The climatic influence of ENSO on rainfall and temperature in the months leading up to and during the outbreak was dramati c, and is likely to contribute to favourable outbreak conditions.