NEW YORK, Aug 17 (Reuters) -- Researchers have found the first direct evidence that a common bacterial infection frequently precedes the onset of heart disease.
Previous studies have suggested that Chlamydia pneumoniae, a bacterium that can cause pneumonia, may also contribute to the development of atherosclerosis, the build-up of fatty plaque in the coronary arteries.
But the findings, published in the August 18th issue of the journal Circulation, provide the first direct evidence that C. pneumoniae infection often precedes atherosclerosis, according to the researchers.
"We were able to add one of the very necessary links in the chain of causality," that could ultimately implicate the bacterial infection in heart disease, lead researcher, Dr. Michael Davidson of the Johns Hopkins University, Baltimore, Maryland, told Reuters Health.
Using high-tech tests, Davidson and colleagues analyzed coronary arteries removed from the bodies of 45 men and 15 women, all Alaska natives who died between the ages of 15 and 57. Most had died in accidents, and very few had been diagnosed with heart disease prior to death. All were indigenous Alaskans, who generally run a lower risk of heart disease than Caucasians.
The researchers also analyzed blood samples that had been taken from the men and women during routine medical exams 8 months to 26 years prior to their deaths. Among other things, the researchers checked the coronary arteries for C. pneumoniae. And they checked the blood samples for antibodies to the bacteria -- evidence of prior infection.
About 37% of the men and women had C. pneumoniae in their coronary arteries, Davidson and colleagues found. Nearly 40% of those with early-stage coronary artery plaques, and 35% of those with more advanced plaques, had the bacteria in these blood vessels, the researchers report. Often, arteries that contained C. pneumoniae bacteria also contained "foam cells," cells that play a key, early role in atherosclerosis, the researchers report. Moreover, Davidson noted that the men and women who had high levels of antibodies to C. pneumoniae in their blood -- suggesting severe infection or repeat infections -- were nearly 10 times as likely to have the bacteria in their arteries as those with few or no antibodies.
The findings suggest that treating people who have severe or chronic C. pneumoniae infections might lower their risks of heart attack, Davidson and colleagues conclude.
But the findings do not suggest that most people should start dosing themselves with antibiotics, Davidson told Reuters Health. Nor do they suggest that people can forget about lifestyle factors that have been shown to contribute to heart disease.
"I wouldn't want people to take this as a message that they could take antibiotics and then stop exercising, or smoke, or eat high-fat diets, or change any of their relationships with known risk factors for atherosclerosis," Davidson said in the interview with Reuters Health.
Previous research suggested that C. pneumoniae might contribute to heart disease by damaging the lining of the coronary arteries, setting the stage for plaque build-up.
SOURCE: Circulation 1998;98.
