Common Infection May Increase Risk of Heart Attack in Seniors
They found that among these older subjects, people who had evidence in the blood of antibodies to the herpes virus were twice as likely as others to have had a heart attack and to have died from heart disease. In contrast, exposure to cytomegalovirus apparently did not increase a person's risk for heart attack, and only those with very high blood levels of antibodies to Chlamydia pneumoniae were at increased risk for heart problems, although the reasons why are unclear.
One expert, though, cautions that antibody levels may not be the most reliable means for determining associations between infection and heart disease. "Antibody [levels] are not very specific in telling who has just been exposed, who is currently infected, or who was chronically infected," says Ignatius W, Fong, MD, professor of medicine at the University of Toronto and head of the division of infectious diseases at St. Michael's Hospital, also in Toronto.
"What you get is a mishmash of patients you look at who may have a combination of previous exposure but are not persistently infected, some who are persistently or chronically infected -- which we think are the ones that will have it in the circulating blood cells and are more at risk for having atherosclerosis -- and the antibody [tests] cannot differentiate them; you can get an overlap and conflicting data from various studies," Fong says.
Siskovick acknowledges that measuring antibody levels essentially gives a snapshot only of prior infections, when "what we're really interested in is chronic infection, reinfection, reactivation of infection, and so on." But because they did not have any way to accurately gauge infections by other means, they designed their study to ask whether previous infection as reflected by the presence of antibodies was related to the risk of heart attack and death from a heart attack in older adults. The signs, Siskovick and colleagues contend, indicate that the answer to that question is probably yes.
In the second study, Ravi Kaul, PhD, associate professor of pediatric infectious disease at the University of California at Davis, looked for evidence of bacterial DNA in cells rather than antibodies in the bloodstream as a sign that a person previously had been infected. They looked for the DNA fingerprints of Chlamydia pneumoniae in immune system cells in 28 patients with coronary artery disease and 19 healthy blood donors.
They found that the bacterial DNA was incorporated into a specific type of immune system cells in 13 of the heart patients and five of the healthy controls. The finding suggests that Chlamydia pneumoniae, which primarily infects lung cells, slips into circulation by piggybacking onto certain immune cells.