Immunoglobulin A antibodies against Chlamydia pneumoniae are associated with expansion of abdominal aortic aneurysm

Background: The aim of this study was to examine the possible association b etween the progression of small abdominal aortic aneurysm (AAA) and chronic infection with Chlamydia pneumoniae. Methods: Patients from a hospital-based mass screening programme for AAA wi th annual follow-up (mean 2.7 years) were included. After initial interview , 139 men aged 65-73 years with a small AAA underwent examination and blood sampling. Immunoglobulin (Ig) G and IgA titres against C. pneumoniae were measured by a microimmunofluorescence test. Results: Some 83 (95 per cent confidence interval 74-93) per cent of the me n had an IgA titre of 20 or more, or an IgG titre of 32 or more. Men with a n IgA titre of 20 or more had a 48 per cent higher AAA expansion rate than those with a titre of less than 20 (3.1 versus 2.1 mm/year; P < 0.05). Mult iple linear and logistic regression analyses showed that an IgA titre of 20 or more was a significant independent predictor of increased AAA expansion , adjusted for known risk factors of expansion. Initial AAA size and serum total cholesterol level were also predictors of expansion. Conclusion: A high proportion of men with a small AAA had signs of chronic infection with C. pneumoniae. Aneurysm progression correlated with evidence of chronic C. pneumoniae infection.