Abstract 18873: Undiagnosed, Unrecognised Influenza is a Risk Factor for Ischemic Vascular Events
Introduction: There is abundant indirect epidemiologic evidence that influenza contributes to all-cause mortality and to cardiac, stroke and respiratory hospitalizations. Many studies show that rates of acute myocardial infarction (AMI) and death increase during the influenza season. In retrospective studies, influenza vaccination is protective against AMI, cardiac death and stroke. However, prospective studies are lacking hence an absence of any direct evidence for a role of influenza in precipitating heart disease and stroke. We assessed the hypothesis that influenza is a significant precipitant of acute ischemic vascular events.
Methods: A prospective case control study in the Australian winter of 2008 and 2009 where 204 cases aged 40 years and older admitted with AMI or stroke to a large teaching hospital were compared to 204 age and sex matched controls from outpatient clinics. Viral nasal and throat swabs were collected at baseline to detect influenza by nucleic acid testing along with a blood sample to measure influenza antibody levels. Another blood sample was collected 4- 6 weeks post recruitment to assess for increases in influenza antibody titers. Serological evidence of influenza was defined as either a baseline result of 64 or greater or a fourfold rise in titer between baseline and convalescent sera in unvaccinated individuals. Subjects with a positive test who received influenza vaccine in the study years were not included in the outcome of interest.
Results: In 408 subjects without respiratory symptoms or obvious respiratory illness, 28 unvaccinated subjects had evidence of influenza infection by PCR or serology. There were 23 positive for influenza among cases (1 by PCR, 22 by serology) and 5 (all by serology) among controls (OR 5.07, 95% CI 1.78-15.56, p<0.0001).
Conclusion: This study shows a significantly higher rate of unrecognized influenza in patients admitted with ischemic vascular events than in control subjects, with the risk of influenza being five times higher. This supports influenza being a precipitant for ischemic vascular events. This also adds to animal models and observational epidemiologic studies which suggest that influenza might cause a pro-thrombotic state and trigger occlusion of already atherosclerotic vessels.
- © 2010 by American Heart Association, Inc.