Incidence of childhood primary immune thrombocytopenic purpura

There is a discrepancy in the reported incidence of childhood immune thrombocytopenic purpura (ITP) between Europe (2.9-5.3 per 100 000 persons) and Japan (1.91). Ise district is a suitable area in which to conduct epidemiological study because there is little fluctuation in the sociodemographic factors. We performed a retrospective population-based study to clarify the incidence of primary childhood ITP. We calculated person-years for children aged <15 years based on the Ise district demographics between 2002 and 2012. The calculated person-years were 298 533. The number of hospitalized patients in Ise district was 25 (M/F, 14/11) during the study period. The calculated incidence was therefore 8.4 per 100 000 person-years. It is possible that the difference in incidence between the present calculation and that of the European studies is due to variation in accuracy and/or registration criteria between the studies.