Lung abscess

Last updated: July 9, 2021

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A lung abscess is a collection of pus within the lung parenchyma. While aspiration of oropharyngeal secretions is the most common cause, lung abscesses can also occur secondary to bronchial obstruction (e.g., malignancy, foreign body aspiration), hematogenous spread (e.g., infectious endocarditis, IV drug use), contiguous spread (e.g., liver abscess), and as a complication of necrotizing pneumonia. The most common causative pathogens are anaerobic bacteria, although aerobic bacteria and, in rare cases, fungi and parasites can also cause lung abscesses. Typical symptoms of a pyogenic lung abscess include fever and cough with production of foul-smelling sputum; they may take weeks or months to develop and may initially be attributed to pneumonia or pulmonary tuberculosis. Lung abscesses typically appear as spherical intraparenchymal cavitary lesions with an air-fluid level on chest imaging. Chest CT is useful for detecting smaller abscesses as well as differentiating abscesses from other cavitary pulmonary lesions. Empiric antibiotic therapy for pyogenic lung abscesses should be started immediately after obtaining relevant cultures and continued for several weeks. Occasionally, percutaneous or bronchoscopic drainage or surgical resection is required. The underlying cause should be evaluated for and treated in all patients.

Reference: [1]

Causative pathogens [1][2][3]

One of the most severe complications of influenza in children and adults is a secondary bacterial infection with Staphylococcus aureus.

Risk factors for lung abscess [1][2][3]


Typically indolent; symptoms can evolve over weeks to months, but may also be acute in onset.

  • Acute: symptoms present for < 4–6 weeks
  • Chronic: symptoms present for > 6 weeks

Characteristic symptoms

Pulmonary examination findings

Reference: [1][2]

General principles [3]

Imaging [1][2]


  • Chest x-ray: typically the initial investigation in any suspected lung pathology
  • CT chest with IV contrast: to confirm the diagnosis and rule out differential diagnoses of lung abscesses [2]


  • Common findings on x-ray and CT
    • Spherical intraparenchymal cavity with thick irregular walls
    • Air-fluid level within the cavity that is dependent on body position
  • Additional findings on CT
  • Location of abscess
    • Due to aspiration: typically unilateral [6]
    • Due to hematogenous dissemination: typically bilateral and multiple [7]

Laboratory studies [1][3]


Additional testing (as needed)

Do not wait for culture results to start antibiotics. Start empirical treatment immediately after obtaining samples for culture, and tailor therapy as needed once culture results are available.

Diagnostics for the underlying cause

As lung abscesses due to aspiration appear in characteristic locations, imaging can help to differentiate them from other cavitary lesions. For example, tuberculosis more commonly affects the lung apices or apical segments of the lower lobes; embolic pulmonary infarcts typically appear as multiple, diffuse lesions. [8]

References: [1][3]

The differential diagnoses listed here are not exhaustive.


  • Admit the patient and start immediate empiric antibiotic therapy (after obtaining samples for culture).
  • Consider the following consults as appropriate:
  • Identify and treat the underlying cause.

Antimicrobial therapy [3][9][10]

Antimicrobial therapy should be tailored to local sensitivities. Follow local guidelines and infectious diseases advice, if available.

Suspected bacterial infection

Bacterial infection is the most common cause of lung abscess and empiric antibiotic therapy should be initiated in all patients with typical clinical features (e.g., fever, purulent sputum) and a cavitary lesion on imaging.

Empiric antibiotic therapy for bacterial lung abscess [3][9][10]
No risk factors for MRSA infection
Suspected MRSA infection

Lung abscesses due to aspiration are typically caused by anaerobic bacteria. Lung abscesses due to hematogenous spread from IV drug use are typically caused by Staphylococcus aureus and streptococci. [7]

Lung abscesses following a recent influenza infection are likely caused by Staphylococcus aureus in children and adults, but can also be caused by Streptococcus pneumoniae and Hemophilus influenzae.

Parasitic or fungal infection [12][13][14]

Suspect parasitic or fungal infection in patients with atypical clinical features (e.g., nonpurulent sputum), an inadequate response to empiric antibiotic therapy, and risk factors (e.g., immunocompromise)

Interventional therapy [1][2][3]

Management of the underlying cause

Examples include:

References: [1][3][15]

We list the most important complications. The selection is not exhaustive.

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