Chlamydia pneumoniae in arteries: the facts, their interpretation, and future studies.

Chlamydiae are small bacteria that, as part of their growth cycle, have an obligate intracellular existence. The small infectious or elementary bodies, about 300 nm in diameter, attach to and are taken into cells where they develop into larger reticulate bodies. These divide by binary fission and are converted into new elementary bodies that are released from the cell. The cycle takes 48 to 72 hours. There are four chlamydial species: Chlamydia psittaci occurs in several diVerent animal species; in humans it causes pneumonia occasionally and abortion rarely. C pecorum is also an animal species, having no known human associations. C trachomatis causes trachoma, as its name implies, and certain serovars cause genital tract disease. C pneumoniae commonly causes a spectrum of lower and upper respiratory tract disease in humans. The first association between this microorganism and coronary heart disease came from a study in Finland, in which it was shown that high titres of IgG and IgA antibodies to C pneumoniae occurred significantly more often in men with myocardial infarction and in those with chronic coronary heart disease than in age matched, randomly selected controls. A metaanalysis of other serological studies has upheld the association between antibody and coronary heart disease, and overall it seems that the relative risk of disease occurring in patients with C pneumoniae antibody is twofold greater than in those without antibody.