The occurrence of stroke in populations is incompletely explained by traditional 
vascular risk factors. Data from several case-control studies and one large 
study using case series methodology indicate that recent infection is a 
temporarily acting, independent trigger factor for ischemic stroke. Both 
bacterial and viral infections, particularly respiratory tract infections, 
contribute to this association. A causal role for infection in stroke is 
supported by a graded temporal relationship between these conditions, and by 
multiple pathophysiological pathways linking infection and inflammation, 
thrombosis, and stroke. Furthermore, observational studies suggest that 
influenza vaccination confers a preventive effect against stroke. Case-control 
and prospective studies indicate that chronic infections, such as periodontitis, 
chronic bronchitis and infection with Helicobacter pylori, Chlamydia pneumoniae 
or Cytomegalovirus, might increase stroke risk, although considerable variation 
exists in the results of these studies, and methodological issues regarding 
serological results remain unresolved. Increasing evidence indicates that the 
aggregate burden of chronic and/or past infections rather than any one single 
infectious disease is associated with the risk of stroke. Furthermore, genetic 
predispositions relating to infection susceptibility and the strength of the 
inflammatory response seem to co-determine this risk. Here, we summarize and 
analyze the evidence for common acute and chronic infectious diseases as stroke 
risk factors.