Space-time clustering of childhood leukaemia cases in Karachi, Pakistan.

T he incidence rate of childhood leukaemia varies internationally (about 4–40/10 per year) with the lowest rates being recorded in black African children. The data from population based studies on the incidence of childhood leukaemia in South Asia, including Pakistan, are lacking. The development of leukaemia has been considered as an infectious process. However, the epidemiological evidence for the existence of childhood leukaemia virus has been regarded as naive. Also, the question whether childhood leukaemias have a tendency to occur in cluster remains unanswered. We conducted this study to determine if clustering of cases of childhood leukaemia at diagnosis in time and time and space if observed was more common than could be expected.