Seasonal incidence of insulin-dependent diabetes (IDDM) in Massachusetts, 1964-1973.

A total of 1142 Massachusetts resident, insulin-dependent diabetics were identified from medical records of the Joslin Clinic. All patients were less than 21 years of age at onset and developed diabetes between 1 January, 1964 and 31 December, 1973. This group consisted of 598 males (52.4%) and 544 females (47.6%) with mean ages at onset (+/- SD) of 11.1 +/- 4.9 and 10.9 +/- 4.6 years respectively. The period between onset and diagnosis was less than two months in 634 cases (81.8%). A first degree family history was noted in 209 cases (18.3%), while an additional 689 cases (60.3%) had more distant relatives with diabetes. The seasonal distribution of onsets was examined in the total group, and in subgroups categorized by sex, type of onset, age of onset, and family history. Significant peaks were noted during the first six months (January-June) in the total group and in all subgroups except those less than five or greater than 14 years of age at onset. Maximum incidence occurred in either January or February. During the second six month period (July-December) strong peaks were noted only in females and in those with no family history. Maximum incidence occurred in late July and in August, respectively. Exceptionally pronounced seasonal variation was demonstrated in a subgroup of 129 diabetics less than 15 years of age with onsets less than two months prior to diagnosis, and with no family history. The distribution of year of onset, in this group, showed considerable variation which did not correlate with year to year fluctuations in the reported incidence of aseptic meningitis, rubeola or mumps.