Relationship between supra-annual trends in influenza rates and stroke occurrence.
BACKGROUND
Stroke occurrence appears to be a random event, yet annual and supra-annual periodicity is observed. Recent attention in atherosclerotic disease etiology has focused on infectious and inflammatory mechanisms. Influenza is one such infection that may influence stroke occurrence.


METHODS
We explored population-based time series data on stroke occurrence and influenza activity. Using Fourier transformation to isolate low-frequency signals in the data, the inverse transformed time series were regressed using Prais-Winsten regression to correct for serially auto-correlated residuals, to assess the relationship between influenza rates and stroke occurrence rates.


RESULTS
Changes in the low-frequency components of influenza activity predicted the changes in low-frequency components of the stroke occurrence data with a delay of about 20 weeks. The delay between changes in influenza activity and subsequent stroke activity was different for different stroke types. Overall, the effect size was small with a tripling of the influenza rate associated with about a 6% change in stroke occurrence rate.


CONCLUSIONS
A small proportion of the patterns of stroke occurrence may be explained by variation in influenza activity. Further evaluation of influenza as a triggering agent in stroke is needed.
Calgary Stroke Program, Department of Clinical Neurosciences, University of Calgary, Calgary, AB T2N 2T9, Canada.
Thalia S
TS
Field
Hongmei
H
Zhu
Michael
M
Tarrant
J Ross
JR
Mitchell
Michael D
MD
Hill
D000293:Adolescent; D000328:Adult; D000368:Aged; D000416:Alberta / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D005583:Fourier Analysis; D006801:Humans; D015994:Incidence; D007251:Influenza, Human / Q000150:complications / Q000453:epidemiology*; D020300:Intracranial Hemorrhages / Q000453:epidemiology* / Q000821:virology; D002546:Ischemic Attack, Transient / Q000453:epidemiology* / Q000821:virology; D008875:Middle Aged; D012621:Seasons; D020521:Stroke / Q000453:epidemiology* / Q000821:virology