C pneumoniae causes pneumonia and bronchitis. The clinical presentation of pneumonia is that of an atypical pneumonia. The organism accounts for approximately 10% of community-acquired pneumonias, ranking second to mycoplasma as an agent of atypical pneumonia. A putative role in coronary artery disease has not held up to close scientific scrutiny.
Like C psittaci, strains of C pneumoniae are resistant to sulfonamides. Erythromycin or tetracycline, 500 mg orally four times a day for 10–14 days, appears to be effective therapy. Fluoroquinolones, such as levofloxacin (500 mg orally once daily for 7–14 days) or moxifloxacin (400 mg orally once daily for 7–14 days), are active in vitro against C pneumoniae and probably are effective. It is unclear if empiric coverage for atypical pathogens in hospitalized patients with community-acquired pneumonia provides a survival benefit or improves clinical outcome.