Two recent trials have shed important light on the theory that the respiratory pathogen Chlamydia pneumoniae might cause atherosclerotic cardiovascular disease.1 2 The first, by Grayston et al, was a trial of azithromycin or placebo taken each week for one year by 4012 patients with stable coronary artery disease who were followed up for four years. The second, by Cannon et al, was a trial of gatifloxacin or placebo taken for 10 days each month for two years by 4162 patients who were in hospital with an acute coronary syndrome. In neither trial did the antibiotic therapy reduce the occurrence of serious cardiovascular events, confirming the conclusion of an earlier meta-analysis of smaller studies.3

Three facts are beyond question in the relation between C pneumoniae and atherosclerosis. Firstly, C pneumoniae DNA and/or antigen have been detected, mainly by polymerase chain reaction technology, in 40% or more of atherosclerotic plaques of patients in various parts of the world, detection being recorded from about the age of 15 onwards.4 Secondly, mice and rabbits inoculated with C pneumoniae have …