ABSTRACT
Background: Seasonal variation has been shown to affect hemorheological mechanisms and blood pressure regulation which may contribute to stroke incidence. An understanding of the seasonal variation of acute stroke may guide the design of a year-long pragmatic acute stroke care plan, especially in regions with meager resources. We investigated the seasonal pattern of acute stroke admissions and outcome in Ibadan, Southwest Nigeria.
Methods: A multi-center retrospective study was performed. Anonymized information on stroke admissions from Jan 01, 2022 – Dec 31, 2022, was extracted from each hospital’s admission records. According to the Nigerian Meteorological Department guidelines, using the average monthly temperatures, the year was divided into the wet (rainy) and dry (harmattan) seasons. The student t-test was used to assess differences between groups. The level of statistical significance was fixed at P<0.05
Results: Of 3001 acute medical admissions, there were 406 (13.5%) acute stroke admissions. Stroke admissions had two peaks: early to mid-wet season and mid-dry season. The proportion of stroke admissions was slightly higher in the wet season 207 (51%) than in the dry season 199 (49%). While stroke admissions, subtype, and outcome did not differ significantly by season, the mean (SD) ischemic stroke count vs hemorrhagic stroke count was slightly higher in the wet season [Ischemic:18.00 (4.15)], hemorrhagic: 18.50 (4.60)] compared to the dry season [ischemic: 14.67 (4.63), hemorrhagic: 16.50 (7.34)], p value 0.218 and 0.584 respectively.
Conclusion: Acute stroke has two seasonal peaks – mid-dry (harmattan) and early to mid-wet seasons. Besides prevailing variations in ambient temperatures and humidity, the bi-annual peaks may also be due to suboptimal risk factor control/surveillance, as the two peaks are incidentally the yuletide seasons in Nigeria. Our findings may therefore help acute care planning during risk periods requiring varying adaptations in local infrastructure and resource allocation.
Keywords: Seasonal variation, Stroke, West Africa, Tropical Africa, Stroke subtype, Seasons