Pneumonia is an infection of the lungs. It affects the lower respiratory tract. This includes small bronchi (airways) 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 (responsible for half of all pneumonias)
• Atypical bacterial pneumonia —often called "walking pneumonia," but can cause a more serious or potentially fatal pneumonia

Other causes of pneumonia include:

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

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, gym)
• Nosocomial pneumonia—acquired during a hospitalization
  • Can be very dangerous, especially for patients on a ventilator
• Aspiration pneumonia —happens when a foreign matter (often stomach content) is inhaled

Factors that increase your chance of pneumonia include:

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

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

The doctor will ask about your symptoms and medical history. A physical exam will be done. Diagnosis is based on symptoms and listening to your chest. Tests may include:

• Chest x-ray —a test that uses radiation to take pictures of structures inside the body, in this case the chest
• CT scan —a type of x-ray that uses a computer to make pictures of structures inside the chest
• Blood tests
• Bronchoscopy —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 of pneumonia depends on:

• Type of pneumonia
• Severity of symptoms
• Other factors

Common treatment approaches include:

• For bacterial pneumonia—antibiotics
• For viral pneumonia—antiviral medicines may be prescribed for young children and people with weakened immune systems
  • Note: Antibiotics are ineffective for treating viral pneumonia.
• Atypical pneumonia—antibiotics

It is very important to take the medicine as prescribed. Stopping medicine early may cause a relapse. It may also create a strain of drug resistant bacteria.

General treatment approaches include:

• Getting plenty of rest and drinking lots of fluids
• Eating a healthy diet (includes lots of fruits and vegetables )—If you do not get enough vitamin C in your diet, ask your doctor if you should take a supplement (up to 1,000 mg). This may be beneficial for some people.
• Taking over-the-counter medicines to reduce fever, aches, and cough
• Being hospitalized (in severe cases)

If you are diagnosed with pneumonia, follow your doctor's instructions .