Background: In the 1980s socioeconomic development was dramatically rapid in the urbanized municipalities of Taiwan due to a prospering economy. This study addressed the question: Could differences in the incidence of childhood leukaemia (age <15) be demonstrated between urban and rural communities in Taiwan between 1981 and 1990?
Methods: The log-linear regression model was used to assess the effects of age, level of urbanization, and calendar year on the variation of childhood leukaemia incidence rates between 1981 and 1990.
Results: Between 1981 and 1990, the overall incidence rate of childhood leukaemia increased by 20% (rate ratio (RR) = 1.2, 95% CI: 1.0-1.5). As compared to rural areas, metropolitan regions showed a significantly higher incidence rate during the study period (RR = 1.3, 95% CI: 1.1-1.6). This urban-rural difference was particularly notable among children <5 years old (RR = 1.5, 95% CI: 1.2-1.9). Dose-response analysis further indicated that risk of childhood leukaemia was monotonically associated with levels of urbanization. The significant gradient in the risk of childhood leukaemia with urbanization was contributed solely by children in the 0-4 years age group.
Conclusions: We noticed a relationship between urbanization and risk of leukaemia in children. Because of a dramatic influx of people into metropolitan areas during the 1980s, our findings may have provided support for the putative association between 'population mixing' or 'population density' and risk of childhood leukaemia. Whether such association can be attributable to virus infection or other aetiologically related leukemogens warrants further investigations.
PIP: A log-linear regression model was applied to national cancer registry data on all childhood leukemia cases diagnosed and reported in Taiwan during 1979-90 in a study to measure the effects of age, level of urbanization, and calendar year upon the variation of childhood leukemia incidence rates between 1981 and 1990. Urban Taiwan underwent a period of rapid socioeconomic development during the 1980s. 1498 cases of leukemia among people under age 15 years were diagnosed during 1981-90 and reported to the Cancer Registry Center of Taiwan. 57.6% of these cases were acute lymphoblastic leukemia, 25.6% were nonlymphoblastic leukemia, and 16.8% were chronic leukemia and those unclassified. Acute lymphoblastic leukemia was the most common subtype in all age groups, with a pronounced peak at 0-4 years. The overall incidence rate of childhood leukemia in Taiwan increased by 20%. When compared to rural areas, metropolitan regions had a significantly higher incidence rate during the study period. That urban-rural difference was especially notable among children under age 5 years. Dose-response analysis further indicated that risk of childhood leukemia was monotonically associated with levels of urbanization. The significant gradient in the risk of childhood leukemia with urbanization was contributed solely by children aged 0-4 years.