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For further information, see CMDT Part 9-11: Pneumonia

Key Features

Essentials of Diagnosis

  • History of or predisposition to aspiration

  • Indolent symptoms, including fever, weight loss, malaise

  • Poor dentition

  • Foul-smelling purulent sputum (in many patients)

  • Opacity in dependent lung zone, with single or multiple areas of cavitation or pleural effusion

General Considerations

  • Nocturnal aspiration of small amounts of oropharyngeal secretions is typically not pathologic

  • Larger aspirations may cause

    • Nocturnal asthma

    • Chemical pneumonitis

    • Bronchiectasis

    • Mechanical obstruction

    • Pleuropulmonary infection

  • Predisposing factors include

    • Drug or alcohol use

    • Seizures

    • Anesthesia

    • CNS disease

    • Trachea or nasogastric tubes

  • Periodontal disease and poor oral hygiene are associated with a greater likelihood of pleuropulmonary infection

  • Disease usually occurs in dependent lung zones

  • Most infections include multiple anaerobic bacteria

    • Prevotella melaninogenica

    • Peptostreptococcus

    • Fusobacterium nucleatum

    • Bacteroides

Clinical Findings

Symptoms and Signs

  • Onset is insidious; necrotizing pneumonia, abscess, or empyema may be apparent at presentation

  • Constitutional symptoms of fever, malaise, and weight loss are common

  • Cough with foul-smelling expectorant suggests anaerobic infection

  • Poor dentition is typical; patients are rarely edentulous

  • Occurrence in an edentulous patient suggests an obstructing bronchial lesion

Differential Diagnosis

  • Other causes of cavitary lung disease

    • Tuberculosis

    • Mycosis

    • Cancer

    • Infarction

    • Necrobiotic nodules in rheumatoid arthritis

    • Pulmonary vasculitidies

  • Fungal infection, eg, histoplasmosis

  • Bronchiectasis


Laboratory Tests

  • Culture of expectorated sputum is not useful due to contamination with oral flora

  • However, a high colony count of a particular microorganism on Gram stain or in culture likely represents a true pathogen

  • Pleural fluid from empyema may be revealing

Imaging Studies

  • Chest radiograph

    • Lung abscess shows a thick-walled cavity surrounded by consolidation, occasionally with an air-fluid level

    • Necrotizing pneumonia demonstrates multiple areas of cavitation within an area of consolidation

  • Empyema is characterized by purulent pleural fluid and may accompany the findings of abscess or necrotizing pneumonia

  • Ultrasonography may identify loculations or help localize fluid for safe thoracentesis

Diagnostic Procedures

  • Representative material for culture can be obtained only by

    • Transthoracic aspiration

    • Thoracentesis

    • Bronchoscopy with a protected brush



  • Medications of choice are directed at anaerobic organisms or facultative anaerobic streptococci and include

    • β-Lactam/lactamase inhibitor combination (eg, amoxicillin/clavulanate; ampicillin/sulbactam; piperacillin/tazobactam)

    • Carbapenem

    • Clindamycin

  • Second-line therapy includes a combination of penicillin and metronidazole

  • Duration of antibiotic therapy for anaerobic pneumonia

    • Usually given for a minimum of 3 weeks

    • Some experts recommend treating until the abscess cavity has resolved on imaging


  • Percutaneous drainage, segmentectomy, lobectomy, or pneumonectomy is rarely required for large abscess

Therapeutic Procedures


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