Background: Previous studies show inconsistent results regarding seasonal variation. The objective of this study was to expand current knowledge on seasonal variation in acute stroke care.

Methods: This nationwide registry-based study comprised data on 132,744 adult patients (≥18 years) with acute stroke (ischemic or hemorrhagic) who were admitted to Swedish hospitals from 2011–2016. Outcomes included quality-of-care indicators and survival, and the exposure variable was month of admission. Unadjusted analyses were followed by logistic regression analyses.

Findings: The unadjusted analyses revealed seasonal variation in patient characteristics, as well as in the quality of care and survival. The adjusted analyses showed significantly higher thrombolysis rates throughout the year with the biggest difference between January and December (OR 1.19, 95% CI 1.08–1.31). Direct stroke unit admission rates were lowest in January and highest in June (OR 1.17, 95% CI 1.09-1.26). Both occupational- and physiotherapist assessment rates within 48 hours were significantly lower in December compared to January (OR 0.85, 95% CI 0.80–0.91, and OR 0.83, 95% CI 0.77–0.88). Door-to-needle times and swallowing test showed no significant monthly variation. 7-, 30- and 90-day survival peaked during the summer and was lowest in the winter, with the biggest difference seen between January and May in 90-day survival (OR 1.28, 95% CI 1.17–1.40). 

Interpretation: Seasonal variation affected the quality of care and survival for stroke patients, and the pattern and magnitude of the effect differed between outcomes. We believe quality improvement efforts should focus on reducing seasonal variation.

ACUTE STROKE PATIENTS ARE SUBJECT TO SEASONAL VARIATION IN QUALITY OF CARE AND SURVIVAL: A SWEDISH NATIONWIDE REGISTRY-BASED STUDY