Atypical pneumonia

Background

Pneumonia caused by organisms not covered by standard beta-lactam antibiotics
Classic atypical organisms: Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila
Frequently presents with more gradual onset and extrapulmonary symptoms compared to typical bacterial pneumonia
Can be difficult to distinguish clinically from typical community acquired pneumonia; many guidelines recommend empiric coverage for both

Gradual onset (days) vs abrupt in typical pneumonia
Dry, nonproductive cough (early — may become productive later)
Prominent extrapulmonary symptoms: headache, myalgias, arthralgias, malaise, pharyngitis
Low-grade fever
Exam may be less impressive than CXR findings (walking pneumonia)
Organism-specific clues:
- Mycoplasma: Young adults, bullous myringitis, erythema multiforme, cold agglutinins
- Legionella: Older adults, smokers; diarrhea, hyponatremia, relative bradycardia, elevated LFTs
- Chlamydophila: Hoarseness, biphasic illness (pharyngitis → pneumonia)

Empiric coverage for atypicals included in standard CAP regimens per guidelines:
- Outpatient (healthy, no comorbidities): Azithromycin or doxycycline monotherapy
- Outpatient (comorbidities): Respiratory fluoroquinolone (levofloxacin or moxifloxacin) OR beta-lactam + macrolide
- Inpatient: Beta-lactam + macrolide OR respiratory fluoroquinolone
See community acquired pneumonia for detailed antibiotic dosing via templates