Chlamydia pneumoniae

Chlamydia pneumoniae is an obligate intracellular bacterium, and must be grown in tissue culture. It is capable of causing persistent infection, often subclinical. It has worldwide distribution and infects many animals as well as humans. Chlamydia pneumoniae is primarily a respiratory pathogen in humans, causing community-acquired pneumonia in all age groups. It can also cause outbreaks in enclosed populations, including military bases, schools, and nursing homes. Chlamydia pneumoniae, as a cause of pneumonia, cannot clinically be differentiated from other causes of atypical pneumonia, especially Mycoplasma pneumoniae. The most accurate method of diagnosis is identification of the organism in respiratory samples by culture or nucleic acid amplification test (NAAT). Serology is of limited value and requires paired sera, and many patients who are positive by culture or NAAT will be seronegative. Chlamydia pneumoniae is susceptible to macrolides, quinolones, and tetracyclines. Data on microbiologic efficacy, including optimal dose and duration of therapy, are limited. The following regimens are clinically effective and result in approximately 80% microbiologic eradication: 10- to 14-day courses of erythromycin, clarithromycin, doxycycline, levofloxacin, or moxifloxacin or 5 days of azithromycin.