AIMS—To find out whether theincidence of infantile hypertrophic pyloric stenosis (IHPS) has changedover the past decade, and if so, to investigate possible contributory factors. METHODS—All infants undergoingpyloromyotomy for IHPS in Sweden between 1987 and 1996 were studied.Using the national patient registers the yearly incidence wasdetermined and evaluated in relation to sex, latitude, urbanisation,and type of surroundings by use of a Poisson model. RESULTS—There was a substantialdecline from 2.7/1000 to 0.85/1000 over the time period. The incidencein the south was almost three times greater than in the north. CONCLUSION—The declining incidenceand geographical difference suggest that environmental factors are ofimportance in this disorder.
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