Basics of Infectious Agents
*The role of this risk factor in the development of heart disease is not yet fully established. While some infectious agents are associated with heart disease and heart attack, it has not yet been shown that treating these infections will lower your risk of having a heart attack or dying early.
What are infectious agents and how are they related to heart disease?
Infectious agents are viruses or bacteria that takes up residence in your body, causing an infection. Certain common infections may play a role in heart disease. The theory is that these bacteria and viruses trigger inflammation in the arteries, making the arteries more likely to become clogged, thereby increasing your risk of heart attack or stroke. Researchers have identified several different bacteria and viruses that may be associated with heart disease.1 The main suspects include:
- Chlamydia pneumoniae (C. pneumoniae), a cause of flu-like respiratory problems that can lead to pneumonia or bronchitis
- Helicobacter pylori (H. pylori), the bacteria that causes stomach ulcers
- Cytomegalovirus (CMV), a member of the herpes family of viruses that usually doesn't cause any symptoms
Studies are currently underway to determine which, if any, of these infections actually increase people's risk for heart disease, heart attack, and death, and whether your risk for heart disease can be reduced by treating these infections. Research so far has had conflicting results, and it's not known whether these infections actually contribute to heart disease or if they are just innocent bystanders. Any links between heart disease and other infections that cause inflammation, such as hepatitis A virus, herpes simplex virus, Epstein-Barr virus, and periodontitis (gum disease), have been less frequently studied.
Are these infections the same as heart infections?
No. Sometimes the heart muscle or the sac that surrounds the heartmay get infected by bacteria causing myocarditis or bacterial pericarditis. This usually happens in people with autoimmune disorders or after a severe chest infection, but it may also be brought on by an allergic reaction to medication. It is one of the reasons that heart patients have to take antibiotics before having dental work done (the bacteria can enter the bloodstream through the cuts in your mouth and travel to the heart to do damage). This is a separate situation and will not be covered in this section.
How common are the 3 infections suspected of causing heart disease?
Very common. Most people will be infected with one of these bacteria or viruses at some point in their lives. The Centers for Disease Control and Prevention estimates that between 50% and 85% of US adults are infected with CMV by age 40.2 About two thirds of the world's population have been infected with H. pylori.3 C. pneumoniae is the most common; it infects about half of all people by age 20 and about 75% by age 60.4
How might these bacteria and viruses cause heart disease?
There are two main theories to explain how these bacteria and viruses may cause atherosclerosis (hardening of the arteries). One is that the bacteria/viruses themselves directly attack and damage artery walls. The other theory is that the presence of these bacteria or virus causes other changes in the body, such as the release of chemicals that can accumulate in the blood vessels and clog the arteries, eventually leading to heart disease.5
A third theory is that the type of infection is less important than the number of different infections you get–a number known as a the total pathogen burden (bacteria and viruses are pathogens).6 In a study of over 1,000 people with heart disease, the number of infections a person had was directly related to their risk of dying from heart disease. People in this study were tested for 8 different infections, including the 3 main suspects. Those who tested positive to more than 5 infections were nearly 5 times more likely to die or have a heart attack than those who tested positive for fewer than 4 infections.7
There are other studies showing a similar connection between the number of infections and heart disease,8-10 but there are also some that don't, including a study of 122 healthy postmenopausal women.11