C. pneumoniae is frequently found in the vessel wall of abdominal aortic aneurysm. The potential etiopathogenetic role of C. pneumoniae in the development of these aneurysms remains to be studied.

The prevalence of chronic Chlamydia pneumoniae infection was assessed in 54 patients with established chronic obstructive pulmonary disease (COPD), 41 of these with severe COPD (group I), 13 with mild to moderate COPD (group II), and in 23 patients with community-acquired pneumonia (controls, group III). Specific IgG and IgA antibody levels and circulating immune complexes (ICs) were measured in paired sera, and specific secretory IgA (sIgA) levels in sputum specimens. A polymerase chain reaction (PCR) test was used for the detection of C. pneumoniae in sputum. According to our definite diagnosis criterion, 65% of the COPD patients showed evidence of suspected chronic C. pneumoniae infection and the prevalence was still higher (71%) in patients with severe disease. The occurrence of specific markers of infection was invariably highest in patients with severe COPD, next-highest in patients with mild to moderate COPD and lowest in pneumonia patients. The association between COPD and C. pneumoniae infection persisted after controlling for the potential confounding factors.

Chlamydia pneumoniae is frequently present in nonrheumatic AVS. Similarly, the high number of C. pneumoniae infections detected in the early lesions of "degenerative" AVS suggest that this pathogen may play an etiologic role in the development of this disease. The validity of this relation requires additional study.

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