Stroke seasonality associations with subtype, etiology and laboratory results in the Ludwigshafen Stroke Study (LuSSt)

Data on seasonal differences in stroke incidence are conflicting. Little is known about seasonal variability in etiological stroke subtypes and population-based data on possible trigger factors are lacking. The Ludwigshafen Stroke Study is a prospective population-based stroke registry. All residents of the city of Ludwigshafen who suffer from acute stroke or TIA are registered. Patients with first-ever stroke (FES) were included for the present analysis. Between January 1, 2006 and December 31st, 2010, 1,779 patients (age 71.7 ± 13.4 years (mean + standard deviation; 897 (50.4 %) women) suffered a FES. Incidence for FES was lowest in summer (reference) with significantly higher rates in winter (rate ratio (RR) 1.20, 95 % confidence interval (CI) 1.05-1.37) and spring (RR 1.21 95 % CI 1.06-1.38). First-ever ischemic stroke (FEIS) was more common in winter (RR 1.16, 95 %CI 1.01-1.34) and first-ever intracerebral haemorrhage (FE-ICH) was more frequent in spring (RR 2.0, 95 %CI 1.24-3.22) than in summer. In FES, systolic and diastolic blood pressure on admission (SBP/DBP) showed significant variation with lowest values in summer (SBP: p = 0.02; DBP p = 0.05). In subtypes of FEIS, cardioembolism tended to be more common in winter (p = 0.14). There were no differences in risk factor prevalence between seasons. Leukocyte count on admission was lowest in summer (8.2 ± 1.4/μl) and highest in winter (8.9 ± 1.9/μl; p = 0.008). The hematocrit showed a similar trend (p = 0.06). Our data show higher incidence rates for FES in winter and spring, for FEIS in winter and for FE-ICH in spring. Variations in blood pressure on admission and leukocyte counts were associated with these findings and may possibly contribute to seasonal stroke variability.