Pneumonia, Anaerobic, & Lung Abscess

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

Diagnosis

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

Treatment

Medications

• 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

Surgery

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

Therapeutic Procedures