Statistical analyses in disease surveillance systems

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

Epidemiological Situation of Dengue Infection in Lao P. D. R.

In 1979, 37 cases of dengue hemorrhagic fever (DHF) were reported to the Ministry of Health for the first time in Laos. In 1985, a total of 1,759 cases of DHF was reported as the first epidemic. In 1987, larger epidemics of DHF occurred with a total of 6,567 cases in the Vientiane Municipality and a total of 3,098 cases in four provinces. The morbidity rate of the outbreak in Vientiane was as high as 1,530/100,000. In the end of 1988, an Aedes Control Unit (ACU) was set up in the Vientiane Municipality to reduce the Aedes larva density and strengthen health education to the residents. Since 1989, DHF epidemic such as seen in 1985 or 1987 has not occurred in Vientiane so far. Activities of the ACU seem to be efficacious in reducing the larva density, judged by the Breteau and House indices obtained. However, another approach to show the reduction of dengue virus transmission has not been tried yet. In 1990, a seroepidemiological study on inhabitants in the Vientiane Municipality was performed. The results indicated followings: (1) The percentage prevalences of neutralizing (N) antibodies to dengue (DEN) 1-4 viruses increased with age, but the prevalences of N antibodies to DEN 3 and DEN 4 were lower than those to DEN 1 and DEN 2 viruses. (2) The geometric mean titer of N antibody to DEN 2 was highest among 4 serotypes in every age group. (3) By the age of 15 years, the majority (90%) of the inhabitants were infected with two or more serotypes of DEN virus