Abstract P425: Influenza-Like Illness as a Risk Factor for Hemorrhagic Stroke

Introduction: Influenza-like illness (ILI) is associated with an increased short-term risk of ischemic stroke. Whether ILI is associated with an increased short-term risk of hemorrhagic stroke remains uncertain. Hypothesis: We hypothesized that ILI would be associated with a heightened risk of hemorrhagic stroke. Methods: We performed a case-crossover analysis utilizing administrative claims data from all emergency department visits and acute care hospitalizations from 2006-2015 in NY and 2005-2015 in FL. We used previously validated International Classification of Disease, Ninth Revision, Clinical Modification codes (ICD-9-CM) to identify patients with ILI and hemorrhagic stroke. Hemorrhagic stroke was defined as the composite of nontraumatic intracranial hemorrhage, nontraumatic subarachnoid hemorrhage, and nontraumatic subdural hemorrhage. We compared the risk of hemorrhagic stroke in successive 30-day periods after ILI versus the corresponding 30-day period one year earlier. We used McNemar test for matched data to calculate the absolute risk increases. Results: We identified 2,838,178 patients with ILI. The absolute increase in hemorrhagic stroke risk was 0.02% (95% confidene interval [CI], 0.02-0.03%) in the thirty days post ILI compared with the same period one year earlier (OR, 3.7; 95% CI, 3.2-4.3). The absolute increase in hemorrhagic stroke risk decreased over successive 30-day periods after ILI and was no longer significant after 180 days post ILI (Figure). Our results were similar when we evaluated the risk of hemorrhagic stroke subtypes separately. Conclusions: ILI is associated with a heightened short-term risk of hemorrhagic stroke. Further studies are warranted to evaluate mechanisms of how infection and/or inflammation lead to a heightened risk of hemorrhagic stroke.