Strong link seen between Chlamydia and heart attack

Certain Chlamydia infections – the kind that cause flu-like respiratory symptoms in thousands of people each year – can be clearly linked to serious heart attacks in relatively young men, according to a new study by UW Medical School researchers and their collaborators at Johns Hopkins University schools of medicine and public health.

Appearing in the current issue of Clinical Infectious Diseases, the study helps clarify sometimes conflicting and inconclusive evidence from previous studies regarding the association between various kinds of infections and coronary heart disease.

Chlamydia pneumoniae is a less known cousin to the sexually transmitted form of Chlamydia (C. trachomatis), but it is far more widespread. Causing a respiratory condition that sometimes progresses to pneumonia, the bacteria spread easily through the air.

The researchers studied the medical records of men in the United States Army between the ages of 30 and 50, identifying 300 of them who had been hospitalized for acute myocardial infarctions. Another set of 300 subjects who hadn’t had heart attacks served as controls.

Stored blood samples for each man were then analyzed.

“The military tests all active-duty personnel every two years for HIV infection and stores the blood specimens in a repository,” explains lead author Christine Arcari, PhD, MPH, assistant professor of population health sciences at UW Medical School. “We analyzed a series of samples over time for each man in our study.”

Since no direct assay exists for Chlamydia pneumoniae, the researchers tested each blood sample for indirect signs of previous infection, looking for two antibodies-IgA and IgG-commonly used to indicate exposure to Chlamydia.

Statistical analysis of the data revealed that high levels of IgA antibodies were independently associated with serious heart attacks. Most previous studies measured the link between heart attacks and only IgG antibodies, which indicate a basic antibody response.

“IgG antibodies are like a long-term memory,” says Arcari, “while IgA is thought to be a more specific marker for recent or chronic infections.”

Analyzing several specimens for each subject over time allowed the researchers to look at the relationship between the time of Chlamydia infection and the risk of heart attacks. They found a stronger association in samples collected one to five years before the cardiac event than in samples collected five or more years before the cardiac event.

“This indicated the possible importance between the time of infection and the date of the cardiac event,” Arcari says.

Such information may help clinicians treat patients accordingly, says co-author Javier Nieto, MD, PhD, chair of the Department of Population Health Sciences at UW Medical School.

Compelling evidence suggests that bacterial infections may trigger inflammatory responses or autoimmune reactions that cause the build-up of atherosclerotic plaques and hardening of the arteries that eventually lead to heart attacks, Nieto says.

The new study’s focus on relatively younger men may help solidify the link between infection and heart attacks, he adds.

“Since Chlamydia infection is so common, by the time people reach 65 years of age, most will have been exposed to it,” he says. “By looking at infection in younger people, we may be able to identify early stages of atherosclerosis.”

Collaborators on the study included Charlotte Gaydos and Kenrad Nelson from Johns Hopkins University and Margot Krauss from Walter Reed Army Institute of Research.