LACK OF EVIDENCE FOR SEASONAL-VARIATION IN EXTRAHEPATIC BILIARY ATRESIA DURING INFANCY

Biliary atresia has been reported anecdotally to occur with temporal a nd geographic clustering suggestive of an infectious etiology. We exam ined the birth dates of infants with extrahepatic biliary atresia (EHB A) during an 18-year period for evidence of a monthly or seasonal dist ribution. Sixty-five patients referred for biliary atresia to the Univ ersity of Michigan over this period were used as index cases. The mont hly and seasonal distributions of birth dates of patients with EHBA we re compared by chi(2) analysis to the monthly and seasonal birth rates of infants born in Michigan (p < 0.77 and p < 0.91, respectively). No significant difference was identified. A power analysis showed that o ur study had an 80% probability of recognizing a 30% variation in birt h rates grouped over a 3-month period. The monthly and seasonal distri butions of conception dates of patients with EHBA were also compared a nd found not to be significantly different from the conception dates o f infants born in Michigan. We conclude that there is no monthly or se asonal variation in the date of birth or the date of conception of inf ants with biliary atresia.