Lack of evidence for seasonal variation in extrahepatic biliary atresia during infancy

Biliary atresia has been reported anecdotally to occur with temporal and geographic clustering suggestive of an infectious etiology. We examined the birth dates of infants with extrahepatic biliary atresia (EHBA) during an 18-year period for evidence of a monthly or seasonal distribution. Sixty-five patients referred for biliary atresia to the University of Michigan over this period were used as index cases. The monthly and seasonal distributions of birth dates of patients with EHBA were 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 our study had an 80% probability of recognizing a 30% variation in birth rates grouped over a 3-month period. The monthly and seasonal distributions of conception dates of patients with EHBA were also compared and found not to be significantly different from the conception dates of infants born in Michigan. We conclude that there is no monthly or seasonal variation in the date of birth or the date of conception of infants with biliary atresia.