Legionellosis differential diagnosis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Legionellosis must be differentiated from other causes of fever, dyspnea, cough, and sputum production, such as bacterial pneumonia, viral pneumonia, and other causes of atypical pneumonia.

Differential Diagnosis

Legionellosis must be differentiated from other causes of fever, dyspnea, cough, and sputum production, such as bacterial pneumonia, viral pneumonia, and other causes of atypical pneumonia.

Disease	Clinical manifestation	Lab findings	Imaging findings	Chest X-ray
Legionellosis	Adult respiratory distress syndrome Bronchial breath sounds Dry cough High grade fever Progressive dyspnea diarrhea nausea, and vomiting	Legionella urinary antigen positive Leukocytosis with relative lymphopenia Hyponatremia Hypophosphatemia	Alveolar consolidation on chest radiograph Lobar consolidation on chest radiograph
Q fever	Abrupt onset of fever, myalgia, headache, and other constitutional symptoms. Cough is the most prominent respiratory symptom and it is usually dry. Cough is associated with dyspnea and pleuritic chest pain.	Antibody detection using indirect immunofluorescence (IIF) is the preferred method for diagnosis. PCR can be used if IIF is negative, or very early once disease is suspected. C. burnetii does not grow on ordinary blood cultures, but can be cultivated on special media such as embryonated eggs or cell culture. A two-to-three fold increase in AST and ALT is seen in most patients.		Q fever pneumonia - - Case courtesy of Royal Melbourne Hospital Respiratory, Radiopaedia.org, rID 21993
Mycoplasma pneumonia	Dry cough Pleuritic chest pain Bronchial breath sounds Inflamed, opaque, hypomobile tympanic membrane	Lymphocytosis Cold agglutinins positivePostitve Coombs test Leukocytosis Thrombocytosis	Alveolar consolidation on chest radiograph Interstitial infiltrate on chest radiograph Lobar consolidation on chest radiograph	Mycoplasma pneumonia - Case courtesy of Dr Alborz Jahangiri, Radiopaedia.org, rID 45781
Chlamydia pneumonia	There are no specific clinical features of chlamydia pneumonia. Symptoms appear gradually. Chlamydia infection is usually associated with upper respiratory tract symptoms (pharyngitis, sinusitis, etc). It might be associated with extrapulmonary maifestations such as meningitis and Guillain-Barre syndrome.	Chlamydia pneumonia is usually associated with normal WBC count. Diagnosed with the presence of antichlamydial antibody (through complement fixation or direct immunofluoroscence) or direct antigen detection.		Chlamydia-pneumonia - Case courtesy of Dr Andrew Dixon, Radiopaedia.org, rID 14567
Acute interstitial pneumonia	Dry cough Progressive dyspnea	Nonspecific	Disseminated consolidation on chest radiograph Interstitial infiltrate on chest radiograph Increased uptake on gallium scan
Pneumococcal pneumonia	High grade fever Hemoptysis Fine rales Pleuritic chest pain Increased breath sounds Bronchial breath sounds Dullness on chest percussion Purulent sputum Shallow respiration Pectoriloquy Increased tactile fremitus Productive cough Egophony	Gram positive diplococci on sputum Gram stain Pleural effusion (exudative) Respiratory alkalosis	Parenchymal hyperlucency on chest radiograph Increased uptake on gallium scan Unilateral diaphragm elevation on chest radiograph Alveolar consolidation on chest radiograph Lobar consolidation on chest radiograph
Pneumocystis carinii pneumonia	Immunosuppressive state Subcutaneous emphysema Hacking cough Progressive dyspnea	Respiratory alkalosis Serum beta-D-glucan elevation	Alveolar consolidation on chest radiograph Lobar consolidation on chest radiograph Interstitial infiltrate on chest radiograph Pneumomediastinum on chest radiograph
Pulmonary embolism	Calf pain or swelling Decreased pulse pressure Dyspnea Hemoptysis Hyperventilation Immobility Increased pulmonic component of heart sound Pleuritic chest pain Prior DVT Pulmonary hypertension Right ventricular heave Right-to-left shunt Substernal chest pain Tachypnea Thrombophlebitis Venous stasis Bone fracture	D-dimer elevation Hypocapnia Hypoxia Pleural effusion (exudative or bloody) Atrial fibrillation on ECG Right axis deviation on ECG Right ventricular overload on ECG	Normal chest radiograph Atelectasis on chest radiograph Lobar consolidation on chest radiograph Prominent pulmonary artery on chest radiograph Hampton's hump on chest radiograph Right ventricular enlargement on echocardiography Thrombus on echocardiography Segmental perfusion defect on lung scan V/Q mismatch on lung scan
Streptococcal pneumonia	Pectoriloquy Bronchial breath sounds Erythema nodosum Purulent sputum Shallow respiration Increased tactile fremitus Pleuritic chest pain Egophony	Gram-positive cocci in chains on sputum Gram stain Respiratory alkalosis Pleural effusion (exudative)	Alveolar consolidation on chest radiograph Lobar consolidation on chest radiograph Empyema on chest radiograph Increased uptake on gallium scan
Viral pneumonia	Pleuritic chest pain Bronchial breath sounds Recent influenza Fine rales Bronchovesicular breath sounds	Lymphocytosis Respiratory alkalosis	Lobar consolidation on chest radiograph Interstitial infiltrate on chest radiograph