Chlamydia pneumoniae infection is associated with coronary artery disease but not implicated in inducing plaque instability

BACKGROUND: Many authors have shown an association between Chlamydia pneumoniae (C. pneumoniae) infection and coronary artery disease. However, whether C. pneumoniae infection plays an important role in triggering an acute coronary event remains to be elucidated. METHODS: Sixty-four consecutive patients with unstable angina (group A), 56 consecutive patients with stable exertional angina (group B) and 74 control subjects (group C) were studied. The IgM, IgG and IgA anti-C. pneumoniae titers were assessed (microimmunofluorescence test Labsystem), values > or =1:16, > or =1:32 and > or =1:16 being respectively considered positive. RESULTS: IgM antibodies were found in 10.9% of group A and 12.5% of group B patients, whereas no subject of group C showed IgM titers (A vs. B, p=ns; C vs. A and B, p<0.05). Positive IgG titers were found in 76.6%, 82% and 44.6% in groups A, B and C, respectively (A vs. B, p=ns; C vs. A and B, p<0.05). Positive IgA titers were found in 62.5%, 61% and 31.1% in groups A, B and C, respectively (A vs. B, p=ns; C vs. A and B, p<0.05). Acute infection was observed in 10.9% and 12.5% of patients in groups A and B, respectively (p=ns); reinfection in 17% and 11%; no patient of the control group had signs of acute infection or reinfection. Chronic infection was observed in 34.4% and 37.5% in group A and B, respectively (p=ns). CONCLUSION: C. pneumoniae infection is associated with coronary artery disease, but no difference in serology is present between unstable and stable angina. Therefore, it does not seem implicated in triggering an acute coronary event.