Bacterial pneumonia differential diagnosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Arooj Naz, M.B.B.S

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Overview

Symptoms related to pulmonary diseases may overlap, and so, it is important to differentiate bacterial causes from other diseases. This can be done with the assistance of laboratory examinations such as chest x-ray findings, throat cultures, and sensitivity bacterial cultures. Some pulmonary diseases that must be differentiated include bronchitis, bronchiolitis obliterans, empyema, lung abscess, and pulmonary carcinomas. Other diseases to be ruled out include bacterial endocarditis, especially in patients with an underlying history of intravenous drug abuse, GERD, and sinusitis.

Differentiating Bacterial Pneumonia from other Diseases

Differential Diagnosis of Pneumonia by Infectious Agent

Disease	Common Organisms
Typical Bacterial	S. pneumoniae, H. influenzae, S. aureus, Klebsiella pneumoniae, anaerobes, group A streptococci, Moraxella catarrhalis
Atypical Bacterial	Mycoplasma pneumoniae, Legionella spp, Chlamydophila pneumoniae, and C. psittaci
Viral	Influenza virus, Parainfluenza virus, Adenovirus, Rhinovirus, RSV, SARS, MERS-CoV
Fungi	Cryptococcus spp, Pneumocystis jirovecii, Histoplasma capsulatum, Coccidioides spp, Aspergillus spp
Parasite

Differential Diagnosis of Pneumonia

Disease	Findings
Acute bronchitis	No infiltrates seen on the chest X-ray
Asthma	Past medical history, no infiltrates seen on chest X-ray
Bronchiolitis obliterans	Should be suspected in patients with pneumonia who do not respond to antibiotics treatment
Congestive heart failure	Bilateral pulmonary edema, shortness of breath
COPD	Past medical history, no infiltrates on chest X-ray, fever is uncommon
Empyema	CXR showing features of pleural effusion, inflammatory markers on thoracocentesis
Endocarditis	Finding of septic pulmonary emboli
Gastroesophageal reflux disease (GERD)	Normal chest X-ray, symptoms are worse during night and associated with meals
Lung abscess	Chest X-ray shows signs of lung abscess
Lung cancer	Weight loss and clear sputum. CT scan and biopsy are helpful in ruling out malignancy
Pertussis	Productive cough for weeks, nasopharyngeal aspirate aids in diagnosis
Pulmonary embolus	A high degree of suspicion should be kept for pulmonary embolus. Chest X-ray may be normal
Sinusitis	Sinus tenderness, post nasal drip
Vasculitis	Systemic manifestations of collagen vascular disease may be seen