Diurnal, weekly, and seasonal variations in stroke occurrence in a population-based study in Auckland, New Zealand.

AIMS: To determine (via a population-based study in Auckland, New Zealand) if there are diurnal, weekly, or seasonal variations in the occurrence of stroke. METHODS: All new stroke events in Auckland residents were traced. Time of onset of the stroke was defined as the time when neurological symptoms were first noticed. The day of the week and month of onset were analysed for all strokes. RESULTS: 1711 patients were registered over 1 year. The rate ratios for the onset of stroke in each 6-hourly interval compared with reference interval (1800-2359 hours) were 0.74 (95% CI: 0.61-1.10) for 0000-0559 hours, 2.88 (95% CI: 2.48-3.34) for 0600-1159 hours and 1.74 (95% CI: 1.49-2.05) for 1200-1759 hours. Rate ratios of the seasonal occurrence of stroke compared with spring were 0.75 (95% CI: 0.65-0.86) for summer, 0.83 (95% CI: 0.73-0.95) for autumn and 1.08 (95% CI: 0.96-1.23) for winter. No weekly pattern of stroke occurrence was observed. CONCLUSIONS: Strokes were less likely to occur during the summer and autumn than in the winter or spring. There was an increase in the occurrence of stroke in the late morning. The results have implications for the provision of acute stroke services in the community and in hospital.