Occurrence of neural tube defects in pregnancy: an excess of cases in a 2773-km2 area in Central Italy.

Neural tube defects (NTDs) have a complex and imperfectly understood etiology, in which both genetic and environmental factors might be involved. The aim of the study was to describe an excess of cases of NTDs in a small area in central Italy. Over a 2-wk period in autumn 2002, three diagnoses of anencephaly were made in a 2773-km(2) area. As a consequence of these events, information on known risk factors as well as data on environmental changes, or epidemics of infectious diseases, in 2002-2004, were collected. The NTD rate was estimated for 10,000 births (live and stillborn) in this area. The 95% confidence intervals of rates were estimated assuming Poisson distribution of cases. Six cases of NTD were observed, with an NTD prevalence rate of 18.5 per 10,000 births (95% CI 17.0, 20.12). No evidence of known risk factors was reported. During summer 2002, the local service for environmental surveillance observed that the threshold level of drinking-water bacterial contamination had been exceeded, which probably resulted in an adjustment in the amount of chlorine added. The major difficulty in making hypotheses regarding the causes of birth defects is linking environmental risk factors exposure to fetal outcome. The prompt gathering of data may be essential. Thus, we emphasize the need for the activation of a population-based congenital malformation registry in order to achieve a deeper understanding of these events etiology.