C. pneumoniae is a common cause of human respiratory diseases, primarily in young adults.

• Seroprevalence rates of 40-70% demonstrate that C. pneumoniae is widespread worldwide. Seropositivity is first detected at school age and then increases by ~10% per decade.
• The role of C. pneumoniae in atherosclerotic disease has long been discussed, but large-scale treatment studies have cast doubts on the etiologic role of this organism in this disease.