Is there any connection between cardiovascular disease and the bacteria Chlamydia pneumonia?

In year 2000, around 14,000 Danes had their first heart attack and almost 3,000 of them died before they reached a hospital. Hence, cardiovascular disease is a serious disorder and many resources have been used for trying to understand the underlying mechanisms of the disease, so that it can be prevented in future.

A heart attack occurs if one or more of the vessels (coronary arteries) that supply oxygen to the heart close. This occurs in places where the coronaries are narrowed due to accumulation of cholesterol in a vessel wall. Such accumulations of cholesterol may be due to hereditary factors, increased cholesterol level, too little exercise, hypertension and smoking.

In a search for the causes for thrombosis in the coronaries, bacteria of the type Chlamydia pneumonia were found in the accumulated cholesterol in the vessel wall in some patients. Chlamydia pneumonia is a normally occurring bacteria which causes pneumonia and which can be treated with macrolide antibiotics (such as erythromycin and clarithromycin) relatively easy.

This gave rise to the question: Is thrombosis in fact an infectious disease caused by Chlamydia pneumonia?

Theoretically, this might very well be true, and especially in patients who get a coronary artery thrombosis without having any of the above-mentioned risk factors.

Because of this, significant research has been conducted within this area over the past 10 years. To clarify whether Chlamydia pneumonia is the cause of thrombosis in the coronaries, a number of very large studies have been carried out.

Patients wishing to participate in these studies were divided into 2 groups by lot. One group was treated with an antibiotic, while the other group had a substance with no effect (placebo). Furthermore, the studies were organised so that neither patients nor doctors knew who were treated with what. By the end of the study, it was calculated whether there was a difference between the 2 groups with regard to the established criteria, such as new heart attacks, death, hospitalisations, etc.

In April 2005, the findings of 11 large studies were gathered. All of these studies were carried out as described above with a total of 19,217 patients, and of these 9,613 were treated with antibiotics and 9,604 with placebo¹ . The patients in these studies had been followed for different periods of time – from 3 months to 4 years. It showed that there were no differences between the two groups – neither beneficial nor harmful.

For further information, please contact Chief Medical Officer Steffen Thirstrup on tel.: +45 4488 9187 / +45 2246 7811 or on sth@dkma.dk.

The Danish Medicines Agency, 8 December 2005

Notes:
JAMA 2005; 293: 2641-7