GEOGRAPHICAL EPIDEMIOLOGY OF HYPOSPADIAS

Abstract

Hypospadias is a urogenital congenital anomaly affecting boys. It appears to have a birth prevalence of between 1 in 10,000 and 1 in 250 male births based on register data which is of limited quality. There are concerns that reported increases in birth prevalence of hypospadias in recent years may point to an important public health risk associated with environmental chemicals, so called endocrine disrupters. This study established a high quality, population based register of hypospadias cases in the North Thames, South Thames and Anglia health districts in the United Kingdom for boys born between 1.1.97 and 30.9.98. Validation was achieved through cross-referencing with Hospital Episode data. The study describes the geographical epidemiology of hypospadias in the study area, within the study period. We employed Quasi-likelihood and Poisson regression to examine the extent to which any spatial heterogeneity might be explained in terms of socio-economic deprivation, rurality, ethnicity and water supply. A register of 732 cases was ascertained from clinical sources in surgical units giving an estimated birth prevalence of hypospadias 38.2 per 10,000 male births. We found evidence (p < 0.001) of spatial heterogeneity and autocorrelation of hypospadias risk at district level (N = 120 districts). Possible ‘clusters’ to the east of the study area were also identified. Regression analysis suggested an association between hypospadias risk and districts with surface (v ground) water supply (indicating water reuse), and an inverse association with districts with >10% and >30% of population of non-white ethnic origin. Odds ratios were 1.57 (95% quasi-likelihood CI 1.17 −2.12), 0.75 (0.61–0.91), and 0.70 (0.52–0.95) respectively. No association was found with socioeconomic deprivation (Carstairs score) and after adjustment for ethnicity, there was a suggestion that hypospadias birth prevalence was lower in more rural districts, possibly reflecting a strong inverse association between rurality and ethnicity. No association with risk of hypospadias was found at postcode level, which may at least be partially explained by migratory effects and misclassification at this level. Crude relative risks at district level varied across the study area from zero to 4.2; after adjustment for water supply (ground/surface) and ethnicity, and with global smoothing using hierarchical Bayesian methods, risk estimates across the area varied from 0.67 to 1.58 and for eight districts there was >95% probability that risk estimates were >1. This study laid the groundwork for further investigation including an ongoing case-control study of hypospadias. The individual level case-control study permits further investigation of the findings of this ecological study, particularly the association found between surface water and hypospadias based on detailed environmental, diet and occupational exposure data collected by telephone interview from cases and controls. The case control study also avoids problems of ecological bias, which may be pertinent to the interpretation of this study.