From the Guidelines
Atypical pneumonia is a type of lung infection caused by organisms different from those that cause typical pneumonia, primarily Mycoplasma pneumoniae, Legionella pneumophila, and Chlamydia pneumoniae, as stated in the guidelines for the management of adults with community-acquired pneumonia 1. The term "atypical pneumonia" refers to the specific pathogens listed above, which can cause pneumonia in patients with no pathogen identified by routine diagnostic testing.
- Symptoms of atypical pneumonia include a persistent dry cough, low-grade fever, headache, fatigue, and mild chest pain.
- For treatment, macrolide antibiotics like azithromycin are first-line therapy, as recommended in the guidelines for the management of community-acquired pneumonia in adults 1.
- Alternatively, doxycycline or fluoroquinolones like levofloxacin may be used.
- Most cases can be treated at home with rest, adequate hydration, and over-the-counter medications for fever and pain.
- Atypical pneumonia differs from typical pneumonia in its presentation, with less severe symptoms, gradual onset, and minimal physical exam findings despite significant X-ray abnormalities.
- These organisms lack cell walls, making them resistant to beta-lactam antibiotics like penicillins and cephalosporins, which is why specific antibiotic choices are crucial for effective treatment, as noted in the guidelines 1. The recommended empirical regimen should routinely cover the 3 most common pathogens that cause severe CAP, all of the atypical pathogens, and most of the relevant Enterobacteriaceae species, as stated in the guidelines for the management of community-acquired pneumonia in adults 1.
From the FDA Drug Label
Atypical pneumonia due to Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila
- Atypical pneumonia is caused by certain bacteria, including:
- Chlamydophila pneumoniae
- Mycoplasma pneumoniae
- Legionella pneumophila Clinical success rates for atypical pneumonia were 96% for Chlamydophila pneumoniae, 96% for Mycoplasma pneumoniae, and 70% for Legionella pneumophila 2
From the Research
Definition of Atypical Pneumonia
Atypical pneumonia is a clinical syndrome characterized by a less severe clinical course than typical bacterial pneumonia, caused by a variety of different organisms including:
- Mycoplasma pneumoniae
- Chlamydiae (such as Chlamydia pneumoniae)
- Rickettsiae
- Viruses
- Legionella pneumophila 3 It is also characterized by systemic complaints rather than respiratory symptoms, with causative pathogens including Mycoplasma, Chlamydia, Legionella, and respiratory viruses (influenza, adenovirus, respiratory syncytial virus) 4.
Causative Organisms
The most common causative organisms of atypical pneumonia are:
- Mycoplasma pneumoniae
- Chlamydia pneumoniae
- Legionella species 5 These organisms are not detectable with Gram stain and cannot be cultured using standard methods.
Treatment
The therapeutic approach for atypical pneumonias is different from that for typical pneumonia, with antibiotics such as macrolides (e.g. erythromycin, azithromycin) or tetracyclines (e.g. doxycycline) being used to treat atypical pneumonia 3, 4. For community-acquired pneumonia, the Japanese pneumonia guidelines propose a differential diagnosis for typical bacterial pneumonia and atypical pneumonia to select an appropriate antibiotic, with a β-lactam drug plus a macrolide or tetracycline, or only fluoroquinolone being considered for elderly individuals and patients with underlying diseases 5. Short-course regimens, such as a 5-day course of levofloxacin, may also be effective in treating atypical community-acquired pneumonia caused by atypical pathogens 6.
Clinical Efficacy
Studies have shown that azithromycin and levofloxacin are effective in treating atypical pneumonia, with high clinical success rates and rapid symptom resolution 7, 6.