Geographic clusters of congenital anomalies in Argentina.

Geographical clusters are defined as the occurrence of an unusual number of cases higher than expected in a given geographical area in a certain period of time. The aim of this study was to identify potential geographical clusters of specific selected congenital anomalies (CA) in Argentina. The cases were ascertained from 703,325 births, examined in 133 maternity hospitals in the 24 provinces of Argentina. We used the spatial scan statistic to determine areas of Argentina which had statistically significant elevations of prevalence. Prenatal diagnosis followed by referral of high-risk pregnancies to high complexity hospitals in a hospital-based surveillance system can create artifactual clusters. We assessed the referral bias by evaluating the prevalence heterogeneity within each cluster. Eight clusters of selected CAs with unusually high birth prevalence were identified: anencephaly, encephalocele, spina bifida, diaphragmatic hernia, talipes equinovarus, omphalocele, Cleft lip with or without cleft palate (CL/P), and Down syndrome. The clusters of Down syndrome and CL/P observed in this study match the previously reported clusters. These findings support local targeted interventions to lower the prevalence of the CAs and/or further research on the cause of each cluster. The clusters of spina bifida, anencephaly, encephalocele, omphalocele, congenital diaphragmatic hernia, and talipes equinovarus may be influenced by prenatal diagnosis and referral to high complexity hospitals.