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Pregnant Women. Pneumonia poses a special hazard for pregnant women, possibly due to changes in a pregnant woman's immune system. This complication can lead to premature labor and increases the risk of death during pregnancy.
Patients With An Impaired Immune System. Pneumonia is particularly serious in people with an impaired immune system. This is especially 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 whose spleen has been 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 potent (virulent) but 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 take time. Severe and life-threatening cases of pneumonia are more likely to occur in elderly people with other medical conditions.
- Streptococcus pneumoniae is the most common cause of pneumonia, as well as all other bacterial upper respiratory infections. It can produce severe pneumonia, with mortality rates of 10%. Nevertheless, pneumococcal pneumonia responds very well to many antibiotics.
- Staphylococcus aureus is a Gram-positive bacterium that often causes severe pneumonia in hospitalized and high-risk patients and following influenza A and B. People who get this form of pneumonia may develop pockets of infection in their lungs (abscesses) that are difficult to treat and can cause the death of lung tissue (necrosis). Mortality rates are 30 - 40%, in part because the patients who develop this infection are generally very ill or vulnerable.
- Pseudomonas aeruginosa and Klebsiella pneumoniae are Gram-negative bacteria that pose a risk for abscesses and severe lung tissue damage.
- Legionella pneumophila can spread easily and cause widespread damage. Treatments have improved dramatically since it was first identified. However, many patients may experience serious problems, including coughing, shortness of breath, fatigue, and nervous system (neurological) and muscle complications.
- Viral pneumonia is usually very mild, but there are exceptions. Respiratory syncytial virus (RSV) pneumonia rarely poses a danger for healthy young adults, but it 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 is more commonly seen with aspiration pneumonia, when a mixture of organisms is carried into the lung. Untreated abscesses can cause hemorrhage (bleeding) in the lung, but targeted antibiotic therapy significantly reduces the danger. Drainage with a needle may also be needed. Abscesses are more common with Staphylococcus aureus, Pseudomonas aeruginosa, or Klebsiella pneumoniae, and are uncommon with Streptococcus pneumoniae.
Respiratory Failure. Respiratory failure is one of the top causes of death in patients with more severe 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 physical changes in the lungs that make it even harder for the lungs to exchange oxygen (ventilatory failure).
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Review Date: 04/13/2010
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine,
Harvard Medical School; Physician, Massachusetts General Hospital.
Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M.,
Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)
