A computer system for epidemiological surveillance

In epidemiological surveillance, it is imperative that any unusual increase in reported cases be detected as quickly as possible. In the surveillance unit at "Pedro Kourí," it was necessary to create a computer system for the surveillance of transmissible diseases in order to manage such variables as morbidity, mortality, and the circulation of causal agents. As usage flexibility is a fundamental requirement, we developed VIGILA as a system readily adaptable to any level of the country's health organizations (national, provincial, or municipal). VIGILA permits the storage, validation, and statistical analysis of morbidity and mortality data, and it also allows the user to apply these features to causal agent information. These manipulations are all performed in the context of a specific transmissible disease. The stored information can be displayed in different types of statistical formats, such as calculated rates, accumulates and medians. The user can also design his/her own tables for display. In addition, the program offers graphics that depict the endemic forecast for a specific region and age group. Reliable forecasts based on temporal models of an epidemiological indicator are necessary for the prediction of the non-epidemic indicator and for the elaboration of an alert threshold. The endemic forecast or endemic channel is calculated by means of a modified version of R. Serfling's model [1] which adapts to data series with stationary characteristics. In this case, the model is fixed for the medical attention protocol and the circulation of agents of a specific transmissible disease. The parameters of the model are estimated by the least square method. The confidence limits are calculated with the T-Student distribution [2]. To enter information about a specific disease and level of health concern, the user must define the disease under analysis, the principal territory under surveillance and its dependencies, the causal agents of the disease, and the frequency with which the disease is reported. This system stores the number of cases (morbidity) and death (mortality) that occurred in the territories and age groups defined during entry. To facilitate the calculation of morbidity and mortality rates, information pertaining to the number of territory habitants and their age groups is also stored. The laboratory data includes the number of analyzed samples in the territories and age groups defined in the data entry, and the samples that were positive to the defined agents. Among the principal uses of the system are: calculation of cumulative cases, rates, and cumulative rates for the specific period of analysis, territory, and age group; comparison of these health indicators with the previous year's indicators or with the median of the previous years' indicators' calculation of the endemic forecast that permits the user to observe the epidemiological situation by territories and age groups; and the early detection of an increase in disease occurrence. The system also offers a geographical representation of the epidemiological situation in the territories, showing a map with the evaluation of each territory with respect to four possible risk factors. VIGILA is available in both DOS and WINDOWS 3.1 formats. This system allows the evaluation of the situation at a specific point in time in the analyzed territories, and may alert the infection control team to an epidemic early enough to allow implementation of control measures.