Abstract. The importance of leptospirosis in Southeast Asia was assessed in conjunction with other studies supported by the U.S. Naval Medical Research Unit No. 2 (US NAMRU-2), Jakarta, Republic of Indonesia. These included studies of hospital-based, acute clinical jaundice in Indonesia, Lao PDR, and Socialist Republic of Vietnam; nonmalarial fever in Indonesia; and hemorrhagic fever in Cambodia. Background prevalence estimates of leptospiral infection were obtained by a cross-sectional, community-based study in Lao PDR. Laboratory testing methods involved serology, microscopic agglutination test, and reverse-transcriptase polymerase chain reaction. Suggestive evidence of recent leptospiral infections was detected in 17%, 13%, and 3% of patients selected on the basis of non-hepatitis A through E jaundice, nonmalarial fever, and hemorrhagic fever (in the absence of acute, dengue viral infections). Leptospiral IgG antibody, reflective of prior infections, was detected in 37% of human sera, collected in Lao PDR. The predominant leptospiral serogroups identified from cases with clinical jaundice were Hurstbridge, Bataviae, and Icterohaemorrhagiae tonkini LT 96 69. Among the nonmalarial febrile cases, Bataviae was the most frequently recognized serogroup. Pyrogenes and Hurstbridge were the principal serogroups among the hemorrhagic fever case subjects. These findings further attest to the relative importance of clinical leptospirosis in Southeast Asia. The wide spectrum of clinical signs and symptoms associated with probable, acute, leptospiral infections contributes to the potential of significant underreporting.

The ecology of hepatitis E virus (HEV) transmission in South-East Asia was assessed from a review of 6 published and 3 unpublished NAMRU-2 reports of hepatitis outbreak investigations, cross-sectional prevalence studies, and hospital-based case-control studies.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.

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Analysis of serum samples from patients with acute jaundice by means of enzyme-linked immunosorbent assay and polymerase chain reaction testing provided the first profile of this condition in Vientiane, Lao PDR, in 1995 and 1996. In a case-control, hospital-based study, evidence of acute infections due to hepatitis A and B viruses was found in 14% and 10% of cases, respectively. Hepatitis E virus, however, did not appear to contribute to clinically recognized acute jaundice. Similarly, antibody to hepatitis C virus was recognized in almost equal proportions of cases (8%) and controls (6%), thus representing probable background infections. The detection of hepatitis G virus marks the first report of this virus in Lao PDR. The large proportion (21%) of new leptospiral infections in cases without acute hepatitis A or B was notable. This finding suggests significant regional underreporting of leptospirosis as a cause of acute jaundice. The limited laboratory diagnostic capabilities for confirming a differential diagnosis of leptospirosis contribute to the lack of attention paid to this important health problem.

The performance of disease surveillance systems is evaluated and monitored using a diverse set of statistical analyses throughout each stage of surveillance implementation. An overview of their main elements is presented, with a specific emphasis on syndromic surveillance directed to outbreak detection in resource-limited settings. Statistical analyses are proposed for three implementation stages: planning, early implementation, and consolidation. Data sources and collection procedures are described for each analysis.During the planning and pilot stages, we propose to estimate the average data collection, data entry and data distribution time. This information can be collected by surveillance systems themselves or through specially designed surveys. During the initial implementation stage, epidemiologists should study the completeness and timeliness of the reporting, and describe thoroughly the population surveyed and the epidemiology of the health events recorded. Additional data collection processes or external data streams are often necessary to assess reporting completeness and other indicators. Once data collection processes are operating in a timely and stable manner, analyses of surveillance data should expand to establish baseline rates and detect aberrations. External investigations can be used to evaluate whether abnormally increased case frequency corresponds to a true outbreak, and thereby establish the sensitivity and specificity of aberration detection algorithms.Statistical methods for disease surveillance have focused mainly on the performance of outbreak detection algorithms without sufficient attention to the data quality and representativeness, two factors that are especially important in developing countries. It is important to assess data quality at each state of implementation using a diverse mix of data sources and analytical methods. Careful, close monitoring of selected indicators is needed to evaluate whether systems are reaching their proposed goals at each stage.

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A total of 141 serum specimens from inhabitants in eight age groups in Vientiane, Lao PDR was examined to estimate the neutralizing anitibody levels to dengue (DEN) and Japanese encephalitis (JE) viruses. From the analyses of the results of neutralization (N) tests, the following conclusions were drawn about the prevalences of DEN and JE viruses in Vientiane: (1) The percentage incidences of N antibodies to DEN 1-4 viruses increased with age, but the incidences of N antibodies to DEN-3 and DEN-4 were lower than those to DEN-1 and DEN-2, which reached 100% by the age of 21-30 years old. (2) The percentage incidence of N antibody to JE virus was similar to those to DEN-3 and DEN-4. (3) The geometric mean titer of N antibody to DEN-2 was highest among four serotypes in every age group, indicating that, in the past, DEN-2 virus was most prevalent. (4) By the age of 15 years old, the majority of the inhabitants (88.2%) in Vientiane were infected with two or more serotypes of DEN viruses and most children seem to be exposed first to DEN viruses and later to JE virus.

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