In the process, they seem to have cleared an infectious agent that many scientists regarded as the most likely suspect -- Chlamydia pneumoniae, which causes lung disease. Instead, they point the finger at a common virus that usually causes no symptoms, and at infections in general.
When they began the study, which looked for antibodies -- evidence of infection -- in blood samples from more than 3,000 people with heart disease or stroke, or at high risk for those condition, the primary target was C. pneumoniae , says Dr. Marek Smieja, an assistant professor in the department of pathology and molecular medicine at McMaster University in Canada. However, three other infectious agents were included in their search, to serve as controls.
Tests found no higher incidence of antibodies against C. pneumoniae in persons who died of heart disease or stroke, says a report on the study in tomorrow's issue of Circulation. The same was true of antibodies to Helicobacter pylori, which causes ulcers, and hepatitis A, a virus that causes liver disease. Unexpectedly, the risk of heart attack or stroke was increased by 24 percent for persons with antibodies to cytomegalovirus (CMV), which strikes between 50 percent and 85 percent of people by the time they reach age 40.
"It is a relatively modest increase," Smieja says. "But our A priority was to find a link to chlamydia, and we didn't."
The study also found that people infected with all four viruses were 41 percent more likely to suffer a heart attack or stroke or die of any cardiovascular disease than those infected with one or no viruses.
"Perhaps not one infection but total exposure to viruses does increase the risk," Smieja says. "The concept of measuring a person for total exposure to infection is alive and well."
From a research point of view, that's true, says Dr. Richard C. Pasternak, an associate professor of medicine at Harvard Medical School and a spokesman for the American Heart Association. But in medical practice, "there is no point in measuring people without heart disease or with heart disease for infectious agents to measure their risk."
"There are three plausible ways an infectious agent could be related to heart disease," Pasternak says. "It could cause the problem. It could facilitate development of the problem by amplifying the effect of other risk factors. Or it could be an aftereffect of the problem, weakening people so they are at higher risk. This is an excellent study, but it doesn't get us closer to understanding which of the three is true."
The two physicians agree on one thing: "At this point, this makes no difference in patient management," Smieja says. "I don't think it has any direct relationship to patient care," Pasternak says."
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