Lung Abscess

Synonyms: Pyogenic lung infection/pneumonia, necrotising pneumonia

Severe, localised suppurative infection in the substance of the lung, associated with necrotic cavity formation. The process is usually surrounded by a fibrous reaction, forming the abscess wall. Multiple small abscess formation may occur and is sometimes referred to as necrotising pneumonia. The most frequent cause is aspiration of anaerobic organisms from the mouth in those predisposed to pulmonary aspiration, with impaired immune defences and cough reflex. A pneumonitis develops which progresses to abscess formation over a period of days or weeks.

• Inhalation of foreign body
• Bacteraemia seeding in the lungs
• Tricuspid endocarditis leading to septic pulmonary embolus
• Extension of hepatic abscess
• Associated with bronchial carcinoma
• Proximal to bronchial obstruction
• Complication of severe or incompletely treated pneumonia (particularly Staphylococci or Klebsiellae)
• Penetrating pulmonary trauma e.g. stab wound

1. Primary abscess - occurs in previously normal lungs and may follow aspiration
2. Secondary abscess - occurs in patients with an underlying lung abnormality

Anaerobic bacteria are involved in about 90% of cases. About half of these are lone anaerobic infection, the other half are mixed with aerobes. Hospital-acquired infections show a higher proportion of Gram-negative bacteria and staphylococci. Community-acquired lung abscesses similarly, are caused mostly by multiple anaerobic bacteria with less aerobic organisms.²

Anaerobes

• Peptostreptococcus spp.
• Bacteroides spp.
• Fusobacterium spp.
• Microaerophilic streptococci

Aerobes

• Staphylococcus aureus
• Streptococcus pyogenes
• Haemophilus influenzae
• Pseudomonas aeruginosa
• Klebsiella pneumoniae- becoming more prevalent³
• Burkholderia cepacia - (formerly classified as a Pseudomonas species; particularly associated with cystic fibrosis)
• Streptococcus pneumoniae
• Actinomyces spp.
• Nocardia spp.
• Proteus mirabilis
• Pasteurella multocida - (zoonotic infection from cats/dogs/cattle)⁴
• Burkholderia pseudomallei - (soil-borne Asian/Australian infection; cases occurred following the tsunami disaster in 2004)⁵

Other organisms

• Mycobacterial infections (predominantly tuberculosis)
• Fungi such as Aspergillus, Cryptococcus, Histoplasma, Blastomyces, Coccidioides
• Parasitic protozoa such as Entamoeba histolytica, Paragonimus

Incidence and prevalence figures have not been established.

Risk Factors

• Alcoholism/drug misuse
• Post-general anaesthesia
• Pneumonia
• Diabetes mellitus
• Choking/near-drowning/aspiration
• Penetrating pulmonary trauma¹
• Severe periodontal disease
• Stroke/cerebral palsy/cognitive impairment/impaired consciousness leading to increased risk of aspiration
• Immunosuppression, particularly chronic granulomatous disease in children
• Congenital heart disease
• Chronic lung disease, particularly cystic fibrosis
• Hepatic abscess/chronic liver disease
• Bacteraemia
• Tricuspid endocarditis

Symptoms

• Onset of symptoms is often insidious (more acute if follows pneumonia)
• Spiking temperature with rigors and night sweats
• Cough ± phlegm production (often foul-tasting and foul-smelling and often blood-stained)
• Pleuritic chest pain
• Breathlessness

Signs

• Tachypnoea
• Tachycardia
• Finger clubbing in chronic cases
• Dehydration
• High temperature
• Localised dullness to percussion (if consolidation also present or effusion)
• Bronchial breathing and/or crepitations (if consolidation present)
• Also look for signs of severe periodontal disease and infective endocarditis

• Other causes of chest infection or pneumonia e.g. Tuberculosis and opportunistic mycobacteria
• Neoplasia e.g. cavitating bronchial carcinoma
• Pulmonary infarction or pulmonary embolism
• Vasculitis e.g. Wegener's granulomatosis
• Sarcoidosis with cavities
• Infected bronchogenic cyst

• FBC - normocytic anaemia or neutrophilia
• Renal function
• Liver function tests
• Blood cultures and sputum cultures (including AAFB)
• ESR/C-reactive protein usually elevated
• Chest X-ray - shows walled cavity, usually with a fluid level; may also be presence of an empyema or effusion
• Tapping or draining of fluid or empyema with microbiology and cytology of samples
• CT scan of thorax - may detect multiple small abscesses
• Fibre optic bronchoscopy can exclude obstruction and provide samples for culture
• Trans-thoracic biopsy/aspiration (usually with ultrasound guidance) or trans-tracheal biopsy

Supportive measures

• Analgesia
• Oxygen if required
• Rehydration if indicated
• Postural drainage with chest physiotherapy

Antibiotics

• Begin with intravenous treatment usually for about 2-3 weeks and follow with oral antibiotics for further 4-8 weeks.
• Recommended first line therapy includes beta lactam/beta-lactam inhibitor or cephalosporin (second or third generation) plus clindamycin.³
  Previously therapy with a broad spectrum penicillin and clindamycin was used. Clindamycin had also been used alone (covers Staphylococcus aureus and anaerobes and both oral and intravenous preparations exist) - however, in the 1990s it was discovered that some anaerobes were resistant to both penicillin and clindamycin.
• An alternative regimen is to begin with a broad spectrum cephalosporin and flucloxacillin.⁶
• Regimen should be altered once organism known.
• If condition fails to resolve, consider bronchoscopy/trans-thoracic drainage/cardiothoracic surgical intervention.⁷
• Surgery is associated with a number of complications such as, empyema and bronchoalveolar air leak and especially so in children.⁶
• Where slow resolution occurs, the possibility of malignancy or unusual organisms must be considered.

These include:

• Empyema
• Pneumatocoele
• Bronchopleural fistula

Overall 80% - 90% cure rate with antibiotic therapy.⁷ Morbidity and mortality more likely to be associated with underlying pathology such as bronchial carcinoma. Other poor prognostic factors include pneumonia, reduced level of consciousness, anaemia and infection with Pseudomonas aeuringosa, Staphylococcus aureus and Klebsiella pneumonia.^8,6