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Cosmos Study

No ‘Season’ for Strokes 

March 7, 2023
Dual-Team Study
Team A:Kersten Bartelt, RNEric Barkley
Team B:Blaine Franklin, PT, DPTAlex Piff

Key Finding

  • Our data show no evidence of a seasonal increase in stroke diagnoses following flu season

Previous studies have shown that patients can have an elevated risk of stroke after a hospital admission or emergency department (ED) visit for influenza-like illness.1,2 Some have suggested that this increased risk may cause a “stroke season” in the three to four weeks following flu season, which typically extends from October to March each year in the United States.3  

To evaluate this claim, we analyzed 149 million hospital admissions and emergency department visits for influenza and stroke from July 2017 through January 2023. We found that while admissions and ED visits for influenza have a clear seasonal trend, the incidence of stroke remains consistent throughout the year, with no evidence of a “stroke season” following influenza season, as shown in Figure 1.  

Figure 1
Percentage of Encounters for Flu or Stroke Diagnoses
Percentage of Encounters for Flu or Stroke Diagnoses
Figure 1. Monthly influenza and stroke hospital admissions and ED visits as a percentage of total hospital admissions and ED visits over time. The slight increase in the percentage of hospital admissions and ED visits for stroke in early 2020 aligns with the period when there were fewer non-COVID hospitalizations and ED visits overall due to the pandemic. 

These data come from Cosmos, a HIPAA-defined Limited Data Set of more than 180 million patients from 190 Epic organizations including 1,123 hospitals and more than 22,500 clinics, serving patients in all 50 states and Lebanon. This study was completed by two teams that worked independently, each composed of a clinician and data scientists. The two teams came to similar conclusions. 

References

  1. Boehme AK, Luna J, Kulick ER, Kamel H, Elkind MSV. Influenza-like illness as a trigger for ischemic stroke. Ann Clin Transl Neurol. 2018;5(4):456-463. Published 2018 Mar 14. doi:10.1002/acn3.545 
  2. Kulick ER, Alvord T, Canning M, Elkind MSV, Chang BP, Boehme AK. Risk of stroke and myocardial infarction after influenza-like illness in New York State. BMC Public Health. 2021;21(1):864. Published 2021 May 5. doi:10.1186/s12889-021-10916-4 
  3. Mackinnon J. Doctor tells Canadian State Media That After Flu Season Comes ‘Stroke Season.’ Blaze Media. https://www.theblaze.com/news/doctor-tells-canadian-state-media-that-after-flu-season-comes-stroke-season. Published 2023 Jan 21. Accessed on 2023 Mar 1.