A lung abscess is a collection of pus in the lung that forms after a microbial infection produces a necrotic cavity in the lung parenchyma.

This infection is usually polymicrobial and typically caused by mouth flora including anaerobic bacteria and Streptococci. Staphylococcus aureus and Klebsiella species have also been implicated in lung abscesses.

This infection usually follows aspiration of mouth flora. Patients with a history of alcohol use disorder or other conditions that impair mental status and may predispose to aspiration are at increased risk for this infection, especially if they have poor dentition. This infection may also result as a complication of routine bacterial pneumonia or of surgery.

Patients who have an obstructing airway lesion or neoplasm, who have undergone intrathoracic surgery, or who are immunocompromised are at higher risk for this infection. Lung abscess may be complicated by bronchopleural fistula or empyema.

Patients frequently present subacutely, with symptoms present for weeks before diagnosis. Many patients have cough with putrid sputum in addition to fevers, night sweats, and weight loss. In a subset of patients, presentation may be much more acute. In one large series, most patients were male and had poor dentition.