Merck Manual

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Abscess in the Lungs


Sanjay Sethi

, MD, University at Buffalo, Jacobs School of Medicine and Biomedical Sciences

Reviewed/Revised Mar 2023

A lung abscess is a pus-filled cavity in the lung surrounded by inflamed tissue and caused by an infection.

  • A lung abscess is usually caused by bacteria that normally live in the mouth and are inhaled into the lungs.

  • Symptoms include fatigue, loss of appetite, night sweats, fever, weight loss, and a cough that brings up sputum.

  • Diagnosis is usually determined with a chest x-ray.

  • People usually need to take antibiotics for several weeks before a lung abscess clears up.

Causes of a Lung Abscess

A lung abscess is usually caused by bacteria that normally live in the mouth or throat and that are inhaled (aspirated) into the lungs, resulting in an infection. Often, gum disease Periodontitis Periodontitis is a severe form of gingivitis, in which the inflammation of the gums extends to the supporting structures of the tooth. Plaque and tartar build up between the teeth and gums and... read more Periodontitis (periodontal disease) is the source of the bacteria that cause a lung abscess.

The body has many defenses (such as a cough) to help prevent bacteria from getting into the lungs. Infection occurs primarily when a person is unconscious or very drowsy because of alcohol or recreational drug use, medication use, sedation, anesthesia, or a disease of the nervous system and is thus less able to cough to clear the aspirated bacteria.

In people whose immune system functions poorly, a lung abscess may be caused by organisms that are not typically found in the mouth or throat, such as fungi or Mycobacterium tuberculosis (the organism that causes tuberculosis Tuberculosis (TB) Tuberculosis is a chronic contagious infection caused by the airborne bacteria Mycobacterium tuberculosis. It usually affects the lungs, but almost any organ can be involved. Tuberculosis... read more Tuberculosis (TB) ). Other bacteria that can cause lung abscesses are streptococci and staphylococci, including methicillin-resistant Staphylococcus aureus (MRSA Methicillin-resistant Staphylococcus aureus (MRSA) Staphylococcus aureus is the most dangerous of all of the many common staphylococcal bacteria. These gram-positive, sphere-shaped (coccal) bacteria (see figure ) often cause skin infections... read more Methicillin-resistant <i > Staphylococcus aureus </i> (MRSA) ), which is a serious infection.

Blockage (obstruction) of the airways also can lead to abscess formation. If the branches of the windpipe (bronchi) are blocked by a tumor or a foreign object, an abscess can form because secretions (mucus) can accumulate behind the obstruction. Bacteria sometimes enter these secretions. The obstruction prevents the bacteria-laden secretions from being coughed back up through the airway.

Usually, people develop only one lung abscess as a result of aspiration Aspiration Pneumonia and Chemical Pneumonitis Aspiration pneumonia is lung infection caused by inhaling mouth secretions, stomach contents, or both. Chemical pneumonitis is lung irritation caused by inhalation of substances irritating or... read more or airway obstruction. If several abscesses develop, they are usually in the same lung. When an infection reaches the lungs through the bloodstream, however, many scattered abscesses may develop in both lungs. This problem is most common among people who inject drugs using unsterile methods (such as dirty needles).

Eventually, most abscesses rupture into an airway, producing a lot of sputum that gets coughed up. A ruptured abscess leaves a cavity in the lung that is filled with fluid and air. Sometimes an abscess ruptures into the space between the lungs and the chest wall (pleural space), filling the space with pus, a condition called empyema Types of fluid Pleural effusion is the abnormal accumulation of fluid in the pleural space (the area between the two layers of the thin membrane that covers the lungs). Fluid can accumulate in the pleural... read more Types of fluid .

Symptoms of a Lung Abscess

Symptoms most commonly start slowly. However, depending on the cause of the abscess, symptoms can occur suddenly. Early symptoms include

  • Fatigue

  • Loss of appetite

  • Sweating during the night

  • Fever

  • A cough that brings up sputum

The sputum may be foul smelling (because bacteria that come from the mouth or throat tend to produce foul odors) or streaked with blood. People may have bad breath. People also may feel chest pain as they breathe, especially if the lining on the outside of the lungs and inside of the chest wall (pleura) is inflamed. Many people have these symptoms for weeks or months before seeking medical attention. These people have chronic abscesses and, in addition to the other symptoms, lose a substantial amount of weight and have daily fever and night sweats. In contrast, lung abscesses caused by Staphylococcus aureus or MRSA can be fatal within days, sometimes even hours.

Diagnosis of a Lung Abscess

  • Chest x-rays

  • Sometimes chest computed tomography (CT)

Doctors may take a sample of sputum and try to grow (culture) the organism causing the abscess, but this test is not useful except to rule out certain organisms.

Any infected fluid in the pleural space (empyema) is sampled and sent to a laboratory for culture.

  • Antibiotics seem ineffective

  • Obstruction of the airways (for example, bronchus blockage by a tumor) is suspected

  • The person's immune system is impaired

If the immune system is impaired, organisms that do not usually cause lung abscesses may be causing the abscess. Unusual organisms must be identified as soon as possible because they are treated differently from the usual organisms that cause lung abscess.

Treatment of a Lung Abscess

  • Antibiotics

Treatment requires antibiotics. Antibiotics are initially given through a vein (intravenously—IV) in most cases and later by mouth when the person's condition has improved and the fever has resolved. Antibiotic treatment continues until the symptoms disappear and a chest x-ray shows that the abscess has cleared up. Such improvement usually requires 3 to 6 weeks of antibiotic therapy, but a longer treatment period may be needed.

When the abscess is thought to be the result of a tumor or a foreign object blocking the airway, bronchoscopy is sometimes used for treatment, such as removing the foreign object.

Occasionally, an abscess that has not responded to antibiotics or an empyema has to be drained through a tube inserted through the chest wall or the nose. The tube may be placed using bronchoscopy or inserted by surgery. Rarely, infected lung tissue may have to be removed surgically. Sometimes an entire section (lobe) of a lung or even an entire lung has to be removed.

Most people are cured. Treatment is less likely to be successful when the person is debilitated or has an impaired immune system or when a bronchus is blocked by a tumor.

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