Seasonal variations in the onset of childhood leukemia/lymphoma: April 1996 to March 2000, Shiraz, Iran.

Infection has long been suspected as a possible factor in the aetiology of leukemia and lymphoma, one of the most common malignancies in children. Since most viral infections have seasonal variations of onset, if seasonal trends in 1 month of diagnosis of leukemia and lymphoma could be proved, this would be supportive evidence for an infectious aetiology. A total of 367 cases in the Hospitals of Shiraz University of Medical Sciences, from April 1996 through March 2000, who were diagnosed as having acute lymphocytic leukemia (ALL), acute myeloblastic leukemia (AML), Burkitt's lymphoma (BL) chronic myeloblastic lymphoma (CML), Hodgkin's disease (HD) or non-Burkitt's type non-Hodgkin's lymphoma (NBNHL) were analysed. The month of appearance of the first symptom and the date of diagnosis were recorded. ALL demonstrated statistically significant monthly variation in the date of appearance of the first symptom (p < 0.05; peak in October) and the date of diagnosis (p < 0.05; peak in November). Seasonal variation was demonstrated in the date of the first appearance of symptoms in BL (p < 0.042), and in the date of diagnosis in AML (p < 0.049). There was no statistically significant seasonal variation in the month of diagnosis for other groups. Analysis based on the date of the first symptoms and the date of diagnosis for ALL patients, using summer-winter ratios, also showed a significant winter excess (p < 0.001). Our data provide modest support for an autumn-winter peak in the diagnosis of childhood ALL, underlying mechanisms that account for these patterns are likely to be complex and need more definitive studies. Copyright 2003 John Wiley & Sons, Ltd.