Abscess of the Lung (Lung Abscess)

How a lung abscess forms

Normally, coughing and the gag reflex keep saliva and food out of the airways. When these defenses are reduced, saliva carrying mouth bacteria can be inhaled into the lungs, usually into the lower back parts of the lungs when lying down. Anaerobic bacteria from the gums cause an infection that destroys tissue over 1 to 2 weeks, leaving a cavity filled with pus.

Less commonly, abscesses form from:

• severe pneumonia with bacteria such as Staphylococcus aureus or Klebsiella
• infected material traveling in the blood, for example from endocarditis or injecting drug use
• a blocked airway from a tumor or inhaled object
• infection of a pre-existing cyst or bronchiectasis

Risk factors

• alcohol use disorder and drug use
• seizures, stroke, dementia and other conditions that affect swallowing (dysphagia)
• general anesthesia or heavy sedation
• severe gum disease or dental infections
• vomiting and reflux
• a weakened immune system
• lung cancer or a blocked airway

Symptoms

Symptoms usually develop over weeks rather than days:

• cough producing thick, foul-smelling or bad-tasting sputum, sometimes in large amounts when the abscess drains into an airway
• fever and chills
• night sweats
• tiredness, loss of appetite and weight loss
• chest pain that worsens with breathing
• shortness of breath
• coughing up blood (hemoptysis)
• bad breath

Diagnosis

• chest X-ray: shows a cavity, often with an air-fluid level
• CT scan of the chest: confirms the abscess, its size and position, and distinguishes it from empyema (pus in the space around the lung)
• sputum tests: Gram stain and cultures. Anaerobic bacteria are hard to grow from sputum
• blood cultures and blood count
• tests for tuberculosis and fungal infections, which can also form cavities
• bronchoscopy: if a tumor, inhaled object or unusual infection is suspected, or the abscess is not improving

Lung cancer can cause a cavity that looks like an abscess, particularly in older smokers, so follow-up imaging is important.

Treatment

Antibiotics

Antibiotics that cover mouth anaerobes, such as amoxicillin-clavulanate or clindamycin, are given, often IV at first. Treatment usually lasts 3 to 6 weeks or more, continuing until the X-ray clears or shows only a small, stable scar. Stopping too early risks relapse.

Drainage and surgery

• postural drainage and chest physiotherapy can help the abscess drain into the airways
• CT-guided drainage through the chest wall for large abscesses that do not respond
• bronchoscopic drainage in selected cases
• surgery to remove part of the lung is rarely needed, mainly for very large abscesses, massive bleeding, or suspected cancer

Treating the cause

• dental treatment for gum disease
• swallowing assessment and therapy
• treatment for alcohol or drug use
• removal of an inhaled object

Complications

• spread of infection into the pleural space (empyema)
• rupture into the airway with spillage to other lung areas
• serious bleeding from the lung
• bronchopleural fistula, an abnormal connection between the airway and the pleural space
• sepsis

Outlook

Most people recover fully with prolonged antibiotics. Recovery is slower in older adults and those with a weakened immune system, very large abscesses, or an underlying blockage such as cancer. A small scar or thin-walled cavity may remain.

Frequently asked questions

What is a lung abscess?

A lung abscess is a cavity in the lung filled with pus, caused by a bacterial infection that destroys lung tissue. It usually develops after mouth bacteria are inhaled into the lungs and causes cough with foul sputum, fever and weight loss.

What causes a lung abscess?

Most are caused by aspiration, inhaling saliva or stomach contents containing mouth bacteria. This is more likely with alcohol or drug use, sedation, seizures, stroke, swallowing problems and poor dental health. Severe pneumonia, blood-borne infection and blocked airways are other causes.

What are the symptoms of a lung abscess?

Common symptoms are a cough with thick, foul-smelling or bad-tasting sputum, fever, night sweats, tiredness, weight loss and chest pain. Some people cough up blood. Symptoms often develop gradually over 1 to 3 weeks or longer.

How long does it take to treat a lung abscess?

Antibiotics are usually needed for 3 to 6 weeks, sometimes longer, until chest imaging shows the abscess has cleared or left only a small scar. Most people feel better within the first 1 to 2 weeks, but completing the full course prevents relapse.

Is a lung abscess serious?

It can be, but most people recover with antibiotics. Complications such as spread to the lining of the lung, heavy bleeding or sepsis are uncommon but serious. Seek urgent care for coughing up blood, severe breathlessness or signs of sepsis.