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Complications of pneumonia that may occur include buildup of fluid in the space between the lung and chest wall (pleural effusion), pockets of pus that form in the space between the lung and chest wall (empyema) or in the lung itself (lung abscess), secondary bacterial lung infection after a viral infection, secondary infection, such as a vaginal infection or infections of the digestive system, because of antibiotic therapy, bacteria in the bloodstream (bacteremia) or throughout the body (septicemia), infection caused by swelling of the covering of the spinal cord (meningitis), infection of a joint caused by spread of bacteria through the bloodstream (septic arthritis), and infection of the heart muscle or the sac surrounding the heart (endocarditis or pericarditis).
Abscesses: Abscesses in the lung are thick-walled, pus-filled cavities that are formed when infection has destroyed lung tissue. They are frequently a result of aspiration pneumonia if a mixture of organisms is carried into the lung. Abscesses can cause hemorrhage (bleeding) in the lung if untreated, but antibiotics that target them have significantly reduced their danger. Abscesses are more common with Staphylococcus aureus or Klebsiella pneumoniae, and uncommon with Streptococcus pneumoniae.
Respiratory Failure: Respiratory failure is one of the important causes of death in patients with pneumococcal pneumonia. Acute respiratory distress syndrome (ARDS) is the specific condition that occurs when the lungs are unable to function and oxygen is so severely reduced that the patient's life is at risk. Failure can occur if pneumonia leads to mechanical changes in the lungs (called ventilatory failure) or oxygen loss in the arteries (called hypoxemic respiratory failure).
Bacteremia: Bacteremia (bacteria in the blood) is the most common complication of pneumococcus infection, although it rarely spread to others sites. Bacteremia is a frequent complication of infection from other gram-negative organisms, including Haemophilus influenzae.
Pleural Effusions and Empyema: The pleura are two thin membranes:
- The visceral pleura cover the lungs.
- The parietal pleura cover the chest wall.
In some cases of pneumonia, the pleura become inflamed, which can result in breathlessness and acute chest pain when breathing.
Also, in about 20% of pneumonia cases there is build-up of the fluid between the pleural membranes that lubricates the lung. (Ordinarily the narrow zone between the two membranes contains only a tiny amount of fluid.)
In most cases, particularly in Streptococcus pneumoniae, the fluid remains sterile (no bacteria are present), but occasionally it can become infected and even filled with pus (a condition called empyema). Empyema is more likely to occur with specific organisms, such as Staphylococcus aureus or Klebsiella pneumoniae infections. The condition can cause permanent scarring.
Collapsed Lung: In some cases, air may fill up the area between the pleural membranes causing the lungs to collapse, a condition called pneumothorax. It can be a complication of pneumonia (particularly Streptococcus pneumoniae) or of some of the invasive procedures used to treat pleural effusion.
Other Complications of Pneumonia: In rare cases, infection may spread from the lungs to the heart and can even spread throughout the body, sometimes causing abscesses in the brain and other organs. Severe hemoptysis (coughing up blood) is another potentially serious complication of pneumonia, particularly in patients with other lung problems such as cystic fibrosis.
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