Insignificant seasonal and geographical variation in incidence of biliary atresia in Japan: a regional survey of over 20 years.
OBJECTIVE
Biliary atresia (BA) is the leading cause of obstructive jaundice in the newborn and the major indication for liver transplantation in Japan. Viral infection has been implicated in its etiology because of seasonality and space clustering. However, this has been controversial among whites. The present study investigates space-time clustering of the incidence of BA in Japan.


METHODS
Birth prevalence rates of BA were analyzed in infants born in Hyogo prefecture between 1985 and 2004 to assess time clustering among 3 seasons. The birth prevalence rates were also analyzed for space clustering between the northern (Hokkaido) and the southern islands (Kyushu) (difference of latitude, 10 degrees ) based on the Japanese Biliary Atresia Society Survey 1996-2004. We compared the prevalence rates between these groups using relative risks (RRs) calculated from 2 x 2 contingency tables.


RESULTS
One hundred nineteen infants were born with BA in Hyogo (1.1/10000 live births). Seasonal clustering in April to July did not significantly differ from that of the reference period (RR, 1.45; 95% confidence interval, 0.93-2.27). Based on Japanese registry data, space clustering between the northern and southern islands did not significantly differ (RR, 1.24; 95% confidence interval, 0.83-1.86).


CONCLUSIONS
Neither seasonal nor spatial clustering was statistically proven in Japan.
Wada
Hidemi
H
Division of Pediatric Surgery, Kobe Children's Hospital, Kobe, Hyogo 654-0081, Japan. wada_kch@hp.pref.hyogo.jp
Muraji
Toshihiro
T
Yokoi
Akiko
A
Okamoto
Tatsuya
T
Sato
Shiiki
S
Takamizawa
Shigeru
S
Tsugawa
Jiro
J
Nishijima
Eiji
E
D001656:Biliary Atresia / Q000175:diagnosis / Q000453:epidemiology*; D016000:Cluster Analysis; D016001:Confidence Intervals; D003710:Demography; D005260:Female; D006306:Health Surveys; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D007564:Japan / Q000453:epidemiology; D008297:Male; D015997:Neonatal Screening; D011153:Population; D012189:Retrospective Studies; D012621:Seasons; D012720:Severity of Illness Index; D017678:Sex Distribution