Twenty-four distinct outbreaks of probable chikungunya (CHIK) etiology were identified throughout Indonesia from September 2001 to March 2003, after a near 20-year hiatus of epidemic CHIK activity in the country. Thirteen outbreak reports were based on clinical observations alone, and 11 confirmed by serological/virological methods. Detailed epidemiological profiles of two investigated outbreaks in Bogor and Bekasi are presented. Human sera were screened using an ELISA for IgM and IgG anti-CHIK antibodies. Additionally, reverse transcriptase PCR and virus isolation were attempted for virus identification. The mean age of cases was 37 +/- 18 years in Bogor and 33 +/- 20 years in Bekasi. There was no outstanding case-clustering, although outbreak-affected households were observed to be geographically grouped within villages. The attack rates in Bogor and Bekasi were 2.8/1000 and 6.7/1000 inhabitants respectively. Both outbreaks started in the rainy season following increased Aedes aegypti and A. albopictus densities.

An outbreak of dengue fever (DF), dengue haemorrhagic fever (DHF), and dengue shock syndrome (DSS) in the city of Palembang, south Sumatra, Indonesia was investigated to (i) validate epidemic occurrence, (ii) confirm dengue virus aetiology and associated serotype(s), (iii) provide a demonstrable measure of community impact, and (iv) identify causative relationship (if any) with climatic El Niño Southern Oscillation (ENSO) influences. Trend analysis 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 monthly mean number of outbreak-related dengue cases over 4 months was 833 (range 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 transmission was observed, evolving from a 5-year cyclic phenomenon to an annual occurrence, often indistinguishable from one year to the next. The proportional distribution of clinical outbreak cases into DF, DHF and DSS diagnostic categories was 24%, 66%, and 10%, respectively. The population aged 10-19 years 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 less severe dengue illness, suggesting that virulence may be, in part, a function of infecting serotype. The climatic influence of ENSO on rainfall and temperature in the months leading up to and during the outbreak was dramatic, and is likely to contribute to favourable outbreak conditions.

The ecology of hepatitis E virus (HEV) transmission in South-East Asia was assessed from a review of 6 published and 3 unpublished NAMRU-2 reports of hepatitis outbreak investigations, cross-sectional prevalence studies, and hospital-based case-control studies. Findings from Indonesia and Viet Nam show epidemic foci centred in jungle, riverine environments. In contrast, few cases of acute, clinical hepatitis from cities in Indonesia, Viet Nam and Laos could be attributed to HEV. When communities in Indonesia were grouped into areas of low (< 40%), medium (40-60%), and high (> 60%) prevalence of anti-HEV antibodies, uses of river water for drinking and cooking, personal washing, and human excreta disposal were all significantly associated with high prevalence of infection. Conversely, boiling of river drinking water was negatively associated with higher prevalence (P < 0.01). The protective value of boiling river water was also shown in sporadic HEV transmission in Indonesia and in epidemic and sporadic spread in Viet Nam. Evidence from Indonesia indicated that the decreased dilution of HEV in river water due to unusually dry weather contributed to risk of epidemic HEV transmission. But river flooding conditions and contamination added to the risk of HEV infection in Viet Nam. These findings attest to a unique combination of ecological and environmental conditions predisposing to epidemic HEV spread in South-East Asia.

A suspected hepatitis outbreak occurred in Bondowoso District, East Java Province, Indonesia, in March-May 1998. An investigation was initiated in April 1998, involving a retrospective review of hospital records, a community-based cross-sectional study, and a health service-based case detection and household follow-up. Sera and epidemiological information were collected from 962 individuals: 235 from 3 outbreak-affected communities along the same rural stretch of river, 101 from community controls living distant from the river, 151 cases detected in health centres, 141 family members of the cases, and 334 subjects from neighbouring families. The prevalence of acute hepatitis E virus (HEV), based on anti-HEV IgM, total antibody (Ig) to HEV and polymerase chain reaction (PCR), was significantly (P < 0.00001) higher (52.4%) among the outbreak communities than among the community controls (3%). The background prevalence of HEV, based on anti-HEV IgG, was also significantly (P < 0.00001) higher (47%) among the outbreak communities than among the community controls (3%). None of the 476 sera screened for anti-HAV (hepatitis A virus) IgM was positive. These results indicate that HEV was the aetiological agent responsible for the outbreak. The overall attack rate (AR) for the 3 outbreak-affected communities surveyed was 19%, with AR determined on the basis of clinically recognized, acute jaundice illness. The usage of river water as primary source for bathing, human-waste disposal, and drinking purposes differed significantly (P < 0.00001) between the communities in outbreak areas and those in non-outbreak areas. There is no significant influence attributed to 'boiling water' on acute HEV. No climatic influences (flooding or drought) predisposed this instance of epidemic HEV transmission. This outbreak represents the first documented evidence of epidemic HEV transmission in Java, Indonesia.

Abstract. In April 2001, a second suspected outbreak of dengue hemorrhagic fever in the easternmost region of Indonesia was investigated in Merauke, a town located in the southeastern corner of Papua, by the Indonesian Ministry of Health and the U.S. Naval Medical Research Unit No. 2. Principal case criteria of hemorrhagic disease provided for a study enrollment of 15 clinically acute and 37 convalescing subjects. Additionally, 32 comparable age/sex controls were selected from neighboring households. Laboratory diagnosis involved three testing methodologies: virus isolation by cell culture, a reverse transcriptase-polymerase chain reaction (RT-PCR) assay, and serologic assays. Antibody (IgM) to dengue virus was detected in 27% of the acute clinical cases, 30% of the convalescing cases, and only 3% of the matched controls. Dengue 3 was the only viral serotype detected from acute serum samples by the RT-PCR. The mean ± SD age of the acute and convalescing cases was 7.8 ± 5.4 years. Overall hospital records accounted for 172 suspected outbreak cases, all urban residents of Merauke with no recent travel history outside the area. The estimated outbreak-associated case fatality rate among all suspected dengue cases was 1.2%. A seven-year retrospective review of hospital records in Merauke showed negligible disease reporting involving hemorrhagic disease prior to the outbreak.