Background: The incidence of inflammatory bowel disease (IBD) seems to be rising. Incidence studies could provide more insight into geographical differences and thereby lead to the identification of etiological factors. The aim of this study was to prospectively assess the incidence of pediatric IBD in the Netherlands from 1999 to 2001, using both an active physician case-reporting registry and a nationwide pathology database.
Methods: All pediatricians in the Netherlands were sent monthly identification cards to be returned if they had diagnosed a new case of IBD in a pediatric patient. Follow-up questionnaires were sent to physicians reporting new cases of IBD. The pathology database contains reports from all cytologic and histologic diagnoses made in the Netherlands. Two independent raters searched the database for new IBD cases. Cases identified from the pathology database were labeled as "probable IBD" and "possible IBD." Cases were cross-checked across databases on the basis of gender, date of birth, date of biopsy, and place of residence. Age-specific incidence rates were calculated for the Dutch population for the year 2000.
Results: Five hundred forty-six probable cases of IBD were identified; 217 cases were labeled as possible. The incidence rate was 5.2 new cases per 100000 children (<18 years) per year. An increase in incidence with age was observed. Only 24% of the cases were ascertained through the clinical registry.
Conclusion: The incidence of IBD cases in the Netherlands is comparable with that reported in other European countries. Epidemiological studies using case reporting by physicians may be underestimates of true incidence rates.