Increased fibrinogen levels are associated with persistent Chlamydia pneumoniae infection in unstable coronary artery disease.

AIM Increased levels of acute phase proteins, e.g., fibrinogen, are related to a poor outcome in unstable coronary artery disease, but the cause of inflammation is unknown. We therefore investigated the prevalence of persistent Chlamydia pneumoniae infection, and its relationship to inflammation in this condition. METHODS AND RESULTS In 256 patients participating in the FRISC trial, evaluating the effects of dalteparin (a low molecular weight heparin) in unstable angina or non-Q wave myocardial infarction, Chlamydia pneumoniae IgA antibody titres and levels of fibrinogen, C-reactive protein and troponin T were determined at inclusion. Increased C. pneumoniae IgA antibody titres were significantly more common in the patients (36%) than in a reference population of similar age (19%); P < 0.001. Raised titres were associated with male gender, increasing age, smoking, and elevated concentrations of fibrinogen, C-reactive protein and troponin T. The association between persistent C. pneumoniae infection and increased fibrinogen levels was independent of other risk factors evaluated in multivariate analysis (P = 0.009). CONCLUSION Persistent C. pneumoniae infection is common in unstable coronary artery disease. The independent association between increased C. pneumoniae IgA antibody titres and fibrinogen levels indicates that chronic infection could be of importance for disease activity.