Association between gastric cancer mortality and nitrate content of drinking water: ecological study on small area inequalities.

The carcinogenic feature of N-nitroso compounds has been well established. Similarly, the transformation of ingested nitrate to N-nitroso compounds in the stomach has been thoroughly documented, nevertheless nitrates' carcinogenic effect has not been proved convincingly in human. The present study was aimed to investigate a population of small villages provided by drinking water with high and widely variable nitrate content (72 mg/l median, 290.7 mg/l 95-percentile concentration). Empirical Bayes estimates for settlement-specific age-, sex-, and year-standardised mortality ratios of gastric cancer (GC) were related to the settlement level average nitrate concentrations in drinking water controlling for confounding effects of smoking, ethnicity and education. The log-transformed average nitrate concentration showed significant positive association with stomach cancer mortality in linear regression analysis (p = 0.014). The settlements were aggregated according to the nitrate concentration into 10-percentile groups and the standardised mortality ratios (SMRs) were calculated. Those groups with higher than 88 mg/l average nitrate concentration showed substantial risk elevation and the log-transformed exposure variables proved to be significant predictors of mortality (p = 0.032) at this level of aggregation also. The association seemed to be fairly strong (r2 = 0.46). Although this investigation constituting an ecological study has certain limitations, it supports the hypothesis that the high level of nitrate in drinking water is involved in the development of GC.

[Epidemiologic study of regional inequalities]. / Területi egyenlötlenségek epidemiológiai elemzése.

The technological achievements of the recent years and the need for more advanced control of the processes within the health sector have supported the geographical epidemiology to become a distinct branch of epidemiology. The combined application of the simple standardized rates, statistical tests and different corrected risk parameters is able to describe the health status for geographically defined, small populations. Several statistical processes have been elaborated to estimate the number of the false positive results and to evaluate the role of chance in predicting the observed geographical pattern. These data completed with the usual risk measures quantify the risk difference within a broader region and determine the actual risk levels for the investigated small areas. The routine data processing system operating as a part of the public health surveillance identifies the high risk areas (the clusters) and without leaving the framework of routine data handling investigates the association between basic exposure data and health risks producing additional data about the nature of the aggregation of health related events. All the spetially varying etiological factors (environmental effects, social status, traditions, regional features of the health sector etc.) are ready to elicit regional alterations in the health status. The aim of the geographical information system is to cover the consequences of the uneven distribution of these factors. Since these kind of etiological factors play significant role in the generation of the most important public health problems in Hungary, and it is known that the small area inequalities are profound for these health impairments, the more extensive application of geographical information systems is expected to improve the efficiency of the control for public health problems and the performance of preventive medicine.