Space-time clustering patterns in childhood leukaemia support a role for infection

Previous studies of space-time clustering in childhood leukaemia have produ ced equivocal and inconsistent results. To address this issue we have used Manchester Children's Tumour Registry leukaemia data in space-time clusteri ng analyses. Knox tests for space-time interactions between cases were appl ied with fixed thresholds of close in space, < 5 km and close in time < 1 y ear apart. Addresses at birth as well as diagnosis were utilized. Tests wer e repeated replacing geographical distance with distance to the Nth nearest neighbour. N was chosen such that the mean distance was 5 km. Data were al so examined by a second order procedure based on K-functions. All methods s howed highly significant evidence of space-time clustering based on place o f birth and time of diagnosis, particularly for all leukaemias aged 0-14 an d 0-4 years, and acute lymphoblastic leukaemia (ALL) 0-4 years. Some result s based on location at diagnosis were significant but mainly gave larger P- values, The results are consistent with an infectious hypothesis. Furthermo re, we found an excess of male cases over females involved in space-time pa irs. We suggest this may be related to genetic differences in susceptibilit y to infection between males and females. These findings provide the basis for future studies to identify possible infectious agents. (C) 2000 Cancer Research Campaign.