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Pneumonia

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of pneumonia.

Prognosis

More than a million people are hospitalized each year for pneumonia, making it the third most frequent reason for hospitalizations (births are first and heart disease is second). Although the majority of pneumonias respond well to treatment, the infection can still be a very serious problem. It kills between 40,000 and 70,000 people each year.

Outlook for High-Risk Individuals

Hospitalized Patients. For patients who require hospitalization for pneumonia, the death rate is between 10 - 25%. If pneumonia develops in patients already hospitalized for other conditions, the rates are even higher. They range from 50 - 70% and are greater in women than in men.

Older Adults. Community-acquired pneumonia is responsible for 350,000 to 620,000 hospitalizations in the elderly every year. Older adults have lower survival rates than younger people. Even when older individuals recover from community-acquired pneumonia, they have higher than normal death rates over the next several years. Elderly people who live in a nursing home or who are already sick are at particular risk.

Very Young Children. About 20% of deaths in stillborn and very young infants are due to pneumonia. Small children who develop pneumonia and survive are at also at risk for developing lung problems in adulthood.

Pregnant Women. Pneumonia poses a special hazard for pregnant women, possibly due to changes in a pregnant woman's immune system. It is a leading cause of a mother's death.

Patients With Impaired Immune Systems. Pneumonia is particularly serious in people with impaired immune systems. This is particularly true for AIDS patients, in whom pneumonia causes about half of all deaths.

Patients With Serious Medical Conditions. Pneumonia is also very dangerous in people with diabetes, cirrhosis, sickle cell disease, cancer, and in those who have had their spleens removed.

Risk by Organisms

Specific organisms vary in their effects. Mild pneumonia is usually associated with the atypical organisms Mycoplasma and Chlamydia . Severe pneumonia is most often associated with a wide range of organisms. Some are very virulent (potent) but are extremely curable, while others are difficult to treat.

• Mycoplasma and Chlamydia are the most common causes of mild pneumonias and are most likely to occur in children and young adults. They rarely require hospitalization when they are appropriately treated, although recovery may still be prolonged. Severe and life-threatening cases are more likely to occur in elderly people with other medication conditions.
• S. Pneumonia is the most common cause of pneumonia and, in fact, all upper respiratory infections. It can produce severe pneumonia, with mortality rates of 10%. Nevertheless, it is very responsive to many antibiotics.
• Staphylococcus aureus is a gram-positive bacterium that often causes severe pneumonia in hospitalized patients and following influenza A and B in high-risk patients. People who get this form of pneumonia may develop pockets of infection in their lungs (abscesses) that are difficult to treat and can cause death of lung tissue (necrosis). Mortality rates are 30% to 40%, in part because the patients who develop this infection are generally very ill or vulnerable.
• Pseudomonas aeruginosa and Klebsiella pneumonia are gram-negative bacteria that pose a risk for abscesses and severe lung tissue damage.
• Legionella pneumophila is very virulent and can cause widespread damage. Treatments have improved dramatically since it was first identified. However, a 2002 study suggested that many patients experience long-term problems, including coughing, shortness of breath, fatigue and neurological and muscular complications.
• Viral pneumonia is usually very mild, but there are exceptions. Pneumonia associated with influenza can be serious. Respiratory syncytial virus (RSV) pneumonia rarely poses a danger for healthy young adults, but can be life threatening in infants and serious in the elderly. 

Complications of Pneumonia

Abscess. An abscess in the lung is a thick-walled, pus-filled cavity that forms when infection has destroyed lung tissue. It typically occurs as a result of aspiration pneumonia, when 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 top 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 (ventilatory failure) or oxygen loss in the arteries (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 that line the chest and lungs:

• 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.

In about 20% of pneumonia cases there is build-up of the fluid between the pleural membranes. Ordinarily the narrow zone between the two membranes contains only a tiny amount of fluid, which lubricates the lungs. This build-up of fluid in the pleural space is known as pleural effusion.

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. This is called pneumothorax . It may be a complication of pneumonia (particularly Streptococcus pneumoniae ) or 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 possibly throughout the body. This can cause 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.

Long Term Effects of Atypical Pneumonias

The pneumonias cased by the atypical organisms Mycoplasma and Chlamydia are usually mild. Some research suggests, however, that these organisms, particularly Chlamydia , may have powerful inflammatory effects in the blood vessels. This effect may have certain adverse long-term consequences even in healthy younger individuals.

Heart Disease and Stroke. Research has suggested that the C. pneumoniae may trigger the immune system to react, causing inflammation in the coronary arteries. Over time, this can cause hardening of the arteries (atherosclerosis). Atherosclerosis can lead to heart attacks and strokes. Studies on a causal relationship between C. pneumoniae and heart disease have been mixed.

C. pneumoniae has been associated with a thickening in the carotid arteries that lead to the brain -- a risk factor for stroke. It is not clear whether the organism poses any significant risk for stroke.

Asthma. Chlamydia pneumoniae , Mycoplasma pneumoniae , and RSV are becoming suspects in many cases of severe adult asthma. One small Australian study found evidence of previous C. pneumoniae infection in 64% of the asthmatic patients tested.

• Review Date: 3/28/2006
• Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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