Infection and risk of ischemic stroke: differences among stroke subtypes

Although prior studies have demonstrated that 25% to 35% of stroke patients have had a recent infection, the role of infection as a risk factor remains unclear. Our aim was to characterize the effect of infectious/inflammatory syndromes on stroke risk.

Case-control and crossover analyses of 233 cases and 363 controls aged 21 to 89 years were performed. Cases were patients hospitalized with a first ischemic stroke at a Los Angeles, California, medical center. Controls were outpatients in the hypertension, diabetes, and general medical clinics. All subjects were administered a neurological examination, an infection/inflammation (I/I) examination, and an interview to elicit recent I/I history at baseline (within several days of stroke onset) and again approximately 2 months later. Three physicians classified subjects by the presence or absence of I/I within 1 month of the index dates, based on findings of the I/I examination, the interview report, and laboratory results.

Infections, either total or specific, were not found more frequently in cases than controls. However, patients with a recent respiratory tract infection suffered more often from large-vessel atherothromboembolic or cardioembolic stroke than did patients without infection (48% vs 24%, P=0.07). The age- and sex-adjusted relative risk estimate for these subtypes was 1.75 (95% CI, 0.86 to 3.55). The risk was notably high for those without stroke risk factors: 4.15 (95% CI, 1.22 to 14.1) for normotensives, 2.71 (95% CI, 1.04 to 7.06) for nondiabetics, and 1.74 (95% CI, 0.74 to 4.07) for nonsmokers. Patients with a recent respiratory infection also had a more severe neurological deficit on admission than those without infection (P=0.05).

Our results suggest that respiratory tract infection may act as a trigger and increase the risk of large-vessel and/or cardioembolic ischemic stroke, especially in those without vascular risk factors.