Atypical pneumonia: Difference between revisions

Latest revision as of 01:39, 21 March 2026

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

Clinical Features

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)

Differential Diagnosis

Causes of Pneumonia

Bacteria

Viral

Common
- Influenza
- Respiratory syncytial virus
- Parainfluenza
Rarer
- Adenovirus
- Metapneumovirus
- Severe acute respiratory syndrome (SARS)
- Middle east respiratory syndrome coronavirus (MERS)
- 2019-nCoV (COVID-19)
Cause other diseases, but sometimes cause pneumonia
- Herpes simplex virus
- Varicella-zoster (VZV)
- Measles
- Rubella
- Cytomegalovirus
- Smallpox
- Dengue

Fungal

Parasitic

Evaluation

CXR: patchy infiltrates, often bilateral; may show diffuse interstitial pattern
Labs: CBC, BMP, procalcitonin
Legionella urinary antigen (only detects serogroup 1 — covers ~70% of cases)
Consider Mycoplasma IgM if diagnosis unclear
Severity scoring: CURB-65 or PSI to guide disposition

Management

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

Disposition

Per CURB-65 or clinical judgment
Most atypical pneumonias are mild and managed outpatient

References

Authors:

@@ Line 1: / Line 1: @@
 ==Background==
-Atypical pneumonia is a type of pneumonia that is not caused by the typical pathogens that classically cause pneumonia, which include Streptococcus pneumoniae, Staphylococcus aureus. Klebsiella pneumoniae, and Haemophilus influenzae. The presentation of atypical pneumonia also differs from that of "typical" pneumonia, in that extra-pulmonary symptoms are more likely present, such as arthralgia, fatigue, fever, headache, myalgia. The organisms most commonly responsible for atypical pneumonia include Chlamydia pneumoniae, Legionella pneumoniae, and, Mycoplasma pneumoniae.
+*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
+==Clinical Features==
+*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)
+==Differential Diagnosis==
+{{Causes of pneumonia}}
+==Evaluation==
+*[[CXR]]: patchy infiltrates, often bilateral; may show diffuse interstitial pattern
+*Labs: CBC, BMP, procalcitonin
+*Legionella urinary antigen (only detects serogroup 1 — covers ~70% of cases)
+*Consider Mycoplasma IgM if diagnosis unclear
+*Severity scoring: [[CURB-65]] or PSI to guide disposition
+==Management==
+*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
+==Disposition==
+*Per [[CURB-65]] or clinical judgment
+*Most atypical pneumonias are mild and managed outpatient
+==See Also==
+*[[Community acquired pneumonia]]
+*[[Pneumonia (main)]]
+*[[Legionella pneumophila]]
+==References==
+<references/>
+[[Category:ID]]
+[[Category:Pulmonary]]