Geospatial analysis of hypospadias and cryptorchidism prevalence rates based on postal code in a Canadian province...

Hypospadias and cryptorchidism are hormone-mediated malformations that occur during male development. Prevalence rates of hypospadias and cryptorchidism are thought to be increasing worldwide. In-utero exposure to endocrine-disrupting chemicals (EDCs) may have a role in the occurrence of these malformations. Our group has reported significant clustering of hypospadias and cryptorchidism at the county level in areas of intense agricultural activity in the Canadian province of Nova Scotia (NS). Finer scale spatial analysis has shown clustering near urban centres.

The objectives of the study were: 1) to perform a granular geospatial analysis of hypospadias and cryptorchidism prevalence, at the postal code level, of all babies born in NS over a 26-year period; and 2) to determine whether there is spatial correlation between these conditions and industries linked to toxic output.

Cases of hypospadias and cryptorchidism were identified based on ICD-10 codes from the Nova Scotia Atlee Perinatal Database with records of all live births in NS between 1988 and 2013. Data were geocoded and mapped based on the three first digits of the maternal postal code (Forward Sortation Area [FSA]). Regional prevalence of congenital anomalies was calculated for each of the 77 FSAs. To identify statistically significant high and low prevalence clusters for each anomaly, Local Morans I was used on the spatial data. Geospatial point data was created for industries linked to toxic output and correlation between clusters of malformations and proximity to these industries was assessed.

During the study period, there were 1045 cases of hypospadias and 993 cases of cryptorchidism. Both hypospadias and cryptorchidism demonstrated statistically significant areas of high prevalence clusters. There was no significant spatial correlation between the local clustering of the congenital malformations and proximity to toxic industries.

Our study shows heterogeneity in the distribution of hypospadias and cryptorchidism, which is consistent with previously published works. In this follow-up, granular geospatial analysis of hypospadias and cryptorchidism prevalence in an area with stable population, we did not confirm the previous findings of high clustering in areas of intense agricultural activity. Furthermore, our analysis did not find high clustering of the congenital malformations in areas near toxic industries to support a clear environmental role in their development. Some of the limitations include underdiagnosis of hypospadias and cryptorchidism (as they both present with a clinical spectrum and are non-life threatening), and limited data currently available on the route of exposure to EDC industries in Nova Scotia.