ISOLATION, CAR OWNERSHIP, AND SMALL-AREA VARIATION IN INCIDENCE OF ACUTE LYMPHOBLASTIC-LEUKEMIA IN CHILDREN

To determine whether increased rates of childhood acute lymphoblastic leukaemia (ALL) which had been reported in isolated areas could be att ributed to higher proportions of households owning cars, ecological an alysis was performed with electoral wards as area units. Previous data were re-analysed using the proportion of households having no car, ta ken from the 1981 census of England and Wales, as an additional explan atory factor. A specialist registry of haematopoietic malignancies cov ering one-third of England and Wales (3270 electoral wards) recorded 4 38 cases of ALL in children diagnosed 1984-89, including 304 in the ch ildhood peak (at ages 1-7 years). Relative risks were derived by Poiss on regression of total childhood ALL and at ages 1-7 years for groups of electoral wards classified by isolation and car ownership. Multivar iable analyses included adjustment for socio-economic status. No evide nce of increased risk of childhood ALL in areas where more households own cars was found. ALL at ages 1-7 years was inversely associated wit h car ownership (risk in wards with least cars relative to those with most cars = 2.28, 95% CI: 1.12-4.64). The associations with geographic isolation persisted after allowing for car ownership (risks for ALL i n young children in isolated relative to built-up areas = 2.19, 95% CI : 1.44-3.33). Levels of car ownership cannot explain the increased rat es of childhood ALL which have been observed in isolated areas. No sup port has been found for a hypothesis relating these excesses to benzen e exposure of children transported in cars. The previous explanation f or the small area variation of childhood ALL in terms of geographical isolation and interpretation in terms of exposure to common infections continues to be justified.