Case-control studies and a few prospective studies have indicated that chronic 
infections may add to the risk of stroke and that acute infections may act as 
trigger factors for stroke. Such chronic infections include periodontal disease, 
infection with Chlamydia pneumoniae or Helicobacter pylori, and chronic 
bronchitis. A causal role of these infectious diseases has not been proved, 
given conflicting study results, possible residual confounding in observational 
studies, and the lack of evidence from interventional trials. Therefore, special 
treatment regimens for stroke prevention based on serologic or genomic evidence 
of infection are not indicated outside of randomized studies at present. 
However, the preliminary available evidence suggests that in patients with 
previous cerebral ischemia, clinically diagnosed chronic infections should be 
taken seriously and should receive the treatment that is indicated according to 
current guidelines. This may include appropriate treatment of moderate or severe 
periodontitis and of chronic bronchitis. Inflammatory parameters (eg, C-reactive 
protein, leukocyte count, fibrinogen) are independently associated with the risk 
of first or recurrent stroke. The question of whether these indexes are causally 
related to stroke or merely represent risk markers is not sufficiently 
clarified. Their use in monitoring individual risk in daily clinical practice is 
limited at present by the lack of clearly defined therapeutic strategies to 
modify these parameters, although statins and other drugs can influence 
inflammatory markers. Observational studies have shown that influenza 
vaccination is significantly and independently associated with a reduced risk of 
stroke and myocardial infarction. Although interventional studies in stroke are 
lacking, it is recommendable that in accordance with current guidelines patients 
with previous vascular disease, including stroke, patients with high risk of 
stroke, and all subjects above age 60, receive an influenza vaccination 
annually.