Dec. 23, 2002 -- For years, investigators have sought to prove that infections cause cardiovascular disease, in the hope that antibiotic treatment can prevent heart attack and stroke. New research shows there may, indeed, be a link, but it is not as strong as previously thought.
A clinical trial involving more than 3,000 people, conducted at Ontario, Canada's McMaster University, looked at four infections and found only one of them -- cytomegalovirus -- to be associated with a higher risk of heart disease. Although several earlier studies suggested a strong link between heart disease and exposure to the bacterial infection that causes pneumonia, no such association was found in this study.
The findings are published in the Jan. 21 issue of Circulation.
"Our estimates of the risk are much more modest than some other studies have suggested," lead researcher Marek Smieja, MD, PhD tells WebMD. "I do still believe there is some connection between infections and heart disease, but this study in no way proves it."
The findings follow another major study, funded by drug manufacturer Pfizer Inc., that threw cold water on the notion that antibiotic treatment protects against heart attacks and strokes. The study found no significant difference in outcome between heart patients with the bacterial infection Chlamydia pneumoniae who were treated with antibiotics and those who were not.
"This is very early data, and there is debate about whether the treatment protocol they used was the right one," Smieja says. "But from a patient management point of view, the evidence suggests there is no benefit to treating with antibiotics, and our study suggests that there is no benefit to even looking for infection."
Smieja and colleagues looked for signs of previous exposure to various infections by studying antibody levels in the blood of 3,168 patients with cardiovascular disease or at risk for the disease participating in a separate study. In addition to Chlamydia pneumoniae and cytomegalovirus (CMV), they also looked for antibodies to Helicobacter pylori, a bacterial infection that causes ulcers, and hepatitis A virus (HAV).
The only germ to show a link was CMV, which increased the risk of heart attack, stroke, and cardiovascular death by about 24%. People who had antibodies to all four of the infections, however, were 41% more likely to suffer a cardiovascular event than those who had antibodies to just one infection or to none.
Another recent study also suggests that the number of infections may be a more important risk factor for hardening of the arteries, or atherosclerosis, than the specific infection. Researchers found that patients with antibodies to six different infections were three times as likely to suffer a heart attack or stroke as those with antibodies to one or fewer.
American Heart Association spokesman Richard Pasternak, MD, says the recent findings argue against the idea that exposure to a particular infection is a big risk factor for heart disease.
"In a sense, this disproves the notion that we are going to find a smoking gun, infectious disease-wise, for atherosclerosis," he tells WebMD. "The lack of a consistent pattern in these studies suggests to me that there is not one agent that is critical. But the finding that having a lot of infections increases risk suggests that anything that causes inflammation may promote atherosclerosis and heart disease."