Murat Kalayoglu of the Massachusetts Eye and Ear Infirmary, Peter Libby of Harvard-affiliated Brigham and Women’s Hospital, and Gerald Byrne of the University of Tennessee Health Science Center searched MEDLINE and considered online resources, texts, meeting abstracts, and expert opinion for the association between Chlamydia pneumoniae and atherosclerosis. They included five types of studies and extracted diagnostic, pathophysiologic, and therapeutic information from the selected literature. “Atherosclerosis causes approximately half of all adult deaths in the Western hemisphere and continues to be a major health problem worldwide,” Kalayoglu, the lead author, said. “Traditional risk factors such as elevated cholesterol clearly contribute to these cardiovascular diseases, but leave some 40 percent of cases unexplained. Recent appreciation of atherosclerosis as a chronic, inflammatory disease has rekindled efforts to examine the role that infectious agents may play in atherogenesis.” Their analysis of the data suggests that Chlamydia pneumoniae, which causes “walking pneumonia,” may contribute to atherosclerosis, also known as hardening of the arteries, and its complications, such as heart attack and stroke.