There is a great deal of interest in that possibility. Several organisms have been implicated, but, thus far, the one supported by the best evidence is an organism that lies between the bacteria and viruses called Chlamydia pneumoniae. This organism is a cause of ordinarily mild to moderately severe pneumonia in individuals of all ages. A variety of studies have supported the relationship between chlamydia infection and arteriosclerosis of the coronary blood vessels of the heart. The evidence includes finding the organism in arteriosclerotic plaques, experimental studies in rabbits, and showing evidence of past infection by studies of antibodies to Chlamydia in the blood of people with coronary heart disease. Additionally, there are a few studies that suggest that administration of antibiotics effective against Chlamydia can reduce the occurrence of coronary heart disease and heart attacks in very high risk populations.

In a study reported in the American Journal of Epidemiology, a group of investigators from several major medical and public health centers reported the results of a study on 14,406 men and women, ages 45 to 64 years, who were followed for up to five years. Those who developed heart attacks or other evidences of severe coronary heart disease during the follow-up period, and controls who did not develop heart attacks, were compared in regard to blood antibody levels against Chlamydia; 256 cases were compared with 540 controls.

There was no significant association between antibody levels in the blood to Chlamydia and the likelihood of developing severe coronary heart diseases or heart attacks. The authors concluded: "overall these results do not provide strong support for the hypothesis that Chlamydia is a risk factor for clinical coronary heart disease (including heart attacks)."

Commentary: There are problems with this study -a relatively small number of heart attacks to analyze, a relatively short follow-up period, and, most important, the main measurement, antibody levels in the blood, may not be a good enough indicator of Chlamydia infection. Nevertheless, it is a solid study and a negative one showing no evidence that Chlamydia is involved in coronary heart disease and heart attacks.

This article is reviewed because of the extensive publicity recently proposing that coronary heart disease may be an infectious disease that can be prevented or treated by antibiotics. It is possible that Chlamydia or other infections could play a role in arteriosclerosis, but it is equally possible that Chlamydia, which is ubiquitous, gets into arteriosclerotic plaques after they are formed and plays no significant role at all in heart attacks.

This article throws a bit of cold water on the Chlamydia hypothesis; still there is a real possibility that Chlamydia or other infections are an important risk factor for arteriosclerosis and heart attacks.

But don’t take the notion that Chlamydia is a major cause of coronary heart disease and heart attacks seriously until we have a lot more data. And, nobody should be taking an antibiotic to prevent coronary heart disease or heart attacks unless they are part of a carefully conducted, approved study carried out by reputable scientific investigators to see if antibiotic treatment is or is not beneficial.

This study looked for evidence that Chlamydia infection causes coronary heart disease. An alternative approach is to treat people with coronary heart disease who have evidence of past Chlamydia and see whether new events (such as fatal or non-fatal heart attacks) can be prevented, Two large studies are in progress; patients are to be treated for one year and results are expected in 2003. A small study of this type was reported in the journal Circulation October 10, 2000. Three hundred twenty patients were involved, one-half of whom received an appropriate antibiotic for three months. During a two-year followup period, no benefit was found - that is, there was no reduction in the number of coronary heart disease events. It was a small study, the treatment period was short, and they could have missed a small benefit - but still, it was a negative study.

Muhlstein, J.B., et al. Randomized secondary prevention trial of Azithromycin in patients with coronary artery disease. Circulation. Vol 102. (October 10) Pgs 1755-1760. 2000.

Nieto, F.J. Chlamydia pneumoniae infection and incident coronary heart disease. American Journal of Epidemiology. Vol 150. (July 15) Pgs 149-156. 1999.