Chlamydial Pneumonia

Chlamydial pneumonia is caused by Chlamydophila pneumoniae, an obligate intracellular bacterium distinct from the sexually transmitted Chlamydia trachomatis. It is a common cause of community acquired atypical pneumonia. The illness is generally mild and self limiting, though it occasionally causes more significant disease, particularly in older adults and those with underlying comorbidity.

Pathophysiology

As an obligate intracellular organism, Chlamydophila pneumoniae cannot be cultured by standard bacteriological techniques. Laboratory confirmation needs cell culture or molecular methods.

Like the other atypical respiratory pathogens, it needs antimicrobial agents with adequate intracellular penetration. Beta lactam antibiotics are ineffective against this organism despite their broad activity against typical bacterial pathogens.

The typical presentation is a gradual onset over several days of mild, non productive or minimally productive cough, low grade fever, sore throat and headache. The illness is frequently mild enough to be managed without specific diagnosis or treatment. Examination findings are often unimpressive relative to any radiographic changes.

A biphasic pattern is sometimes described, with initial pharyngitis and laryngitis followed one to several weeks later by lower respiratory tract symptoms. Considerable overlap with other atypical and typical pneumonia presentations makes the causative organism unreliable to identify clinically.

More severe disease, including pneumonia requiring hospital admission, occurs particularly in older patients and those with underlying cardiopulmonary comorbidity. The illness is generally milder than Legionella or typical bacterial pneumonia.

Polymerase chain reaction testing on respiratory specimens (nasopharyngeal swab, sputum) is the most sensitive and specific diagnostic method where testing is pursued.

The illness is generally mild and self limiting, so specific microbiological confirmation is frequently not obtained in routine practice. Empirical treatment with atypical pathogen coverage is sufficient in most community managed presentations.

Serology (paired acute and convalescent samples showing a significant rise in specific antibody titre) can confirm the diagnosis retrospectively. It has limited utility for guiding acute management because of the delay in obtaining convalescent results.

Chest radiography, where performed, shows non specific patchy infiltrates without features distinguishing it from other causes of atypical pneumonia.

Macrolide antibiotics are first line, given their reliable activity and generally favourable tolerability against this organism.

• Azithromycin 500 mg once daily on day one, followed by 250 mg once daily for a further four days (a standard five day course).
• Clarithromycin 500 mg twice daily for 10 to 14 days.

Doxycycline 100 mg twice daily for 10 to 14 days is an effective alternative. It is particularly useful where macrolide resistance is a concern or in patients unable to tolerate macrolide therapy.

Fluoroquinolones (levofloxacin 500 mg once daily, or moxifloxacin 400 mg once daily) are a further alternative with reliable activity. They are generally reserved for more severe disease, treatment failure with first line agents, or where broader empirical coverage is needed because the causative organism is uncertain at the start of treatment.

The illness is frequently mild and self limiting, and presentation overlaps substantially with other community acquired atypical pneumonia. Empirical treatment covering atypical pathogens, as part of standard combination community acquired pneumonia regimens, is therefore generally sufficient. Specific microbiological confirmation of Chlamydophila pneumoniae is not needed in most routine presentations.

Supportive care accompanies antibiotic treatment: adequate hydration, rest and antipyretics as needed. Prognosis is generally favourable, as the course is typically milder than several other atypical and typical bacterial causes of community acquired pneumonia.