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.