Clusters of birth defects: emergency and management. A review of some publications.

Published reports of clusters of congenital anomalies, traditionally defined as an aggregation in time and/or space of malformed cases, are interesting to analyse in terms of emergence, management and initiator of a public health decision. Through some examples of clusters for which a suspected source has been suggested, for those having identified important causal relationship or for those where the cluster appeared without any explanation, the paper shows the different steps that were taken after the initial 'alarm' and the time spent between the alarm and a final conclusion. If basic keys such as accurate field investigation, reliable estimation of the expected number and etiological evaluation, are the rule, the handling should remain flexible to take into account the particularity of each cluster. Among the clusters of congenital anomalies published in the last 20 years, very few of them were clearly explained.