Definition

Pneumonia is an infection of the lungs. There are several different organisms that may cause it.

Causes

Pneumonia affects the lower respiratory [2] tract (small bronchi and air sacs in the lungs). There are three main causes:

• Bacterial pneumonia—caused by bacteria, most commonly Streptococcus pneumoniae
• Viral pneumonia—caused by a virus
  
  • Viruses cause half of all pneumonias.
• Atypical bacterial pneumonia [3]—caused by mycoplasmas, chlamydias, or other tiny infectious agents that have traits of both bacteria and viruses
  
  • This type of pneumonia, often called "walking pneumonia," is thought of as a milder pneumonia. However, each of these infectious agents has the potential to cause a more serious or potentially fatal pneumonia.

Other causes of pneumonia include:

• Fungal infections, such as Pneumocystis carinii pneumonia [4] (PCP)—a fungal infection common in people with AIDS [5]

Pneumonias are sometimes described by where it was acquired and how you were exposed to it:

• Community-acquired pneumonia—acquired in the community (eg, at school, work [6], gym etc.)
• Nosocomial pneumonia—acquired during a hospitalization
  
  • It can be very dangerous, especially for patients on a ventilator.
• Aspiration pneumonia [7]—happens when a foreign matter (often stomach content) is inhaled

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

Risk factors include:

• Age: 65 or older
• Flu [8] or other respiratory [2] illness
• Chronic illness, such as heart [9] or lung disease
• Stroke [10] (aspiration pneumonia due to difficult swallowing)
• Weakened immune [11] system caused by AIDS or chemotherapy [12] treatment
• Chronic bronchitis [13]
• Malnutrition
• Pregnancy
• Infants and very young children
• Alcohol or drug abuse
• Smoking
• Chronic exposure to certain chemicals (eg, work [6] in construction or agriculture)

Symptoms

Symptoms of pneumonia may include some or all of the following:

Diagnosis

The doctor will ask about your symptoms and medical [17] history, and perform a physical exam. Diagnosis is based on symptoms and listening to your chest with a stethoscope. Tests may include:

• Chest x-ray [18]—a test that uses radiation to take pictures of structures inside the body, in this case the chest
• CT scan [19]—a type of x-ray that uses a computer to make pictures of structures inside the chest
• Blood tests
• Bronchoscopy [20]—direct examination of airways
• Sputum culture—testing mucus coughed up from deep in the lungs
• Pulse oximetry—measures the amount of oxygen in the blood
• Arterial blood gas—measures oxygen, carbon dioxide, and acid in the blood

Treatment

Treatment of pneumonia depends on:

• Type of pneumonia
• Severity of symptoms
• Other factors

Common methods of treatment include:

Prevention

Certain vaccines may prevent pneumonia:

Flu shot [21]—for people at high risk, particularly the elderly, because pneumonia may be a complication of the flu [22]

Pneumococcal vaccine [23]—recommended for people over aged 65, or those who have a chronic illness, such as diabetes [24] or sickle-cell disease [25], and children under two years old

Other preventive measures include:

• Avoid smoking. Smoking weakens the lungs' resistance to infection.
• Avoid close contact with people who have respiratory [2] infections.
• Wash hands often when coming in contact with infected people.
• Protect yourself from exposures on the job that affect the lungs.
• Eat a healthy diet.
• Get adequate rest.
• Exercise regularly.