Pneumonia is an infection of the lungs. Many different organisms can cause it, including bacteria, viruses, and fungi.

Pneumonia is a common illness that affects millions of people each year in the United States.

Bacterial pneumonias tend to be the most serious and, in adults, the most common cause of pneumonia. The most common pneumonia-causing bacterium in adults is Streptococcus pneumoniae (pneumococcus).

Respiratory viruses are the most common causes of pneumonia in young children, peaking between the ages of 2 and 3. By school age, the bacterium Mycoplasma pneumoniae becomes more common.

In some people, particularly the elderly and those who are debilitated, bacterial pneumonia may follow influenza or even a common cold.

Many people contract pneumonia while staying in a hospital for other conditions. This tends to be more serious because the patient's immune system is often impaired due to the condition that initially required treatment. In addition, there is a greater possibility of infection with bacteria that are resistant to antibiotics.

See also:

• Aspiration pneumonia
• Atypical pneumonia
• CMV pneumonia
• Hospital-acquired pneumonia
• Legionella pneumonia
• Pneumocystis carinii pneumonia
• Pneumonia in immunocompromised host
• Viral pneumonia
• Walking pneumonia

The main symptoms of pneumonia are:

• Cough with greenish or yellow mucus; bloody sputum happens on occasion
• Fever with shaking chills
• Sharp or stabbing chest pain worsened by deep breathing or coughing
• Rapid, shallow breathing
• Shortness of breath

• Headache
• Excessive sweating and clammy skin
• Loss of appetite
• Excessive fatigue
• Confusion , especially in older people

If you have pneumonia, you may be working hard to breathe, or may be breathing fast. Crackles are heard when listening to your chest with a stethoscope. Other abnormal breathing sounds may also be heard through the stethoscope or via percussion (tapping on your chest wall).

The following tests may show signs of pneumonia:

• Chest x-ray
• Gram's stain and culture of your sputum to look for the organism causing your symptoms
• CBC to check white blood cell count; if high, this suggests bacterial infection
• Arterial blood gases to check how well you are oxygenating your blood
• CAT scan of the chest
• Pleural fluid culture if there is fluid in the space surrounding the lungs

If the cause is bacterial, the goal is to cure the infection with antibiotics. If the cause is viral, typical antibiotics will NOT be effective, however sometimes your doctor may use antiviral medication. In some cases it is difficult to distinguish between viral and bacterial pneumonia, so antibiotics may be prescribed.

Many people can be treated at home with antibiotics. If you have an underlying chronic disease, severe symptoms, or low oxygen levels, you will likely require hospitalization for intravenous antibiotics and oxygen therapy. Infants and the elderly are more commonly admitted for treatment of pneumonia.

You can take these steps at home:

• Drink plenty of fluids to help loosen secretions and bring up phlegm.
• Get lots of rest. Have someone else do household chores.
• Control your fever with aspirin or acetaminophen. DO NOT give aspirin to children.

When in the hospital, respiratory treatments to remove secretions may be necessary. Occasionally, steroid medications may be used to reduce wheezing if there is an underlying lung disease.

With treatment, most patients will improve within two weeks. Elderly or debilitated patients who fail to respond to treatment may die from respiratory failure.

Empyema or lung abscesses are infrequent, but serious, complications of pneumonia. They occur when pockets of pus form around or inside the lung. These may sometimes require surgical drainage.

Call your doctor if you have:

• Worsening respiratory symptoms
• Shortness of breath, shaking chills, or persistent fevers
• Rapid or painful breathing
• A cough that brings up bloody or rust-colored mucus
• Chest pain that worsens when you cough or inhale
• Night sweats or unexplained weight loss
• Signs of pneumonia and weak immune system, as with HIV or chemotherapy

Infants with pneumonia may not have a cough. Call your doctor if your infant makes grunting noises or the area below the rib cage is retracting while breathing.

• Wash your hands frequently, especially after blowing your nose, going to the bathroom, diapering, and before eating or preparing foods.
• Don't smoke. Tobacco damages your lung's ability to ward off infection.
• Wear a mask when cleaning dusty or moldy areas

Vaccines can help prevent pneumonia in children, the elderly, and people with diabetes, asthma, emphysema, HIV, cancer, or other chronic conditions:

• Pneumococcal vaccine (Pneumovax, Prevnar) prevents Streptococcus pneumoniae.
• Flu vaccine prevents pneumonia and other infections caused by influenza viruses. It must be given yearly to protect against new viral strains.
• Hib vaccine prevents pneumonia in children from Haemophilus influenzae type b.

Taking deep breaths may help prevent pneumonia if you are in the hospital -- for example, while recovering from surgery. Often, a breathing device will be given to you to assist in deep breathing.

If you have cancer or HIV, you should talk to your doctor about additional ways to prevent pneumonia.

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Cohen J, Powderly WG. Infectious Diseases. 2nd ed. New York, NY: Elsevier, 2004.

Mandell, GL, Bennett JE, Dolin R, eds. Principles of Infectious Diseases. 5th ed. New York, NY: Churchill Livingstone, 2000.

Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007 Mar 1;44 Suppl 2:S27-72.

American Thoracic Society. Guidelines for the management of adults with hospital-acquired, ventilator-associated, and healthcare-associated pneumonia. Am J Respir Crit Care Med. 2005 Feb 15;171(4):388-416.