Written by Bree Normandin | Published on August 7, 2012
Medically Reviewed by Brenda B. Spriggs, MD, MPH, FACP

What Is Pneumonia?

Pneumonia is an infection in one or both lungs. The infection may be caused by fungi, bacteria, or viruses. Pneumonia causes inflammation in your lung’s air sacs, also referred to as alveoli. The alveoli fill with fluid or pus, making it difficult to breathe. Symptoms of pneumonia can range from mild to life threatening. In fact, pneumonia causes more deaths worldwide than any other illness. The severity of pneumonia usually depends on the cause of the inflammation or by the type of organism causing the infection, a person’s age, and their general health.

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The Types of Pneumonia, Grouped by Causes

There are five major types of pneumonia. They are:

Bacterial Pneumonia

Bacterial pneumonia can affect anyone at any age. It can develop on its own or after a serious cold or flu. The most common cause of bacterial pneumonia is streptococcus pneumoniae. Bacterial pneumonia can also be caused by Chlamydophila pneumonia or legionella pneumophila. Pneumocystis jiroveci pneumonia is sometimes seen in those who have weak immune systems, due to illnesses like AIDS or cancer.

Viral Pneumonia

In most cases, respiratory viruses can cause pneumonia, especially in young children and the elderly. Pneumonia is usually not serious and lasts a short time. However, the flu virus can cause viral pneumonia to be severe or fatal. It’s especially harmful to pregnant women or individuals with heart or lung issues. Invading bacteria can cause complications with viral pneumonia.

Mycoplasma Pneumonia

Mycoplasmas are not viruses or bacteria, but they have traits common to both. They are the smallest agents of disease that affect humans. Mycoplasmas generally cause mild cases of pneumonia, most often in older children and young adults.

Other Types of Pneumonia

Many additional types of pneumonia affect immune-compromised individuals. Tuberculosis and pneumocystis carinii pneumonia (PCP) generally affect persons with AIDS. In fact, PCP can be one of the first signs of illness in people with AIDS.

Less common types of pneumonia can also be serious. Pneumonia can be caused by inhaling food, dust, liquid, gas, and by various fungi.

Who Is at Risk for Developing Pneumonia?

No one is immune to pneumonia, but there are certain factors that can raise your risks:

  • previous stroke or problems swallowing: People who have had a stroke, have problems swallowing, or are bedridden can easily develop pneumonia.
  • age: Infants from birth to age two are at risk for pneumonia, as are individuals age 65 or older.
  • weakened immune system: This includes people who take medications (steroid drugs and anti-cancer drugs) that weaken the immune system and people with HIV, AIDS, or cancer.
  • drug abuse: This includes excessive alcohol consumption and smoking.
  • certain medical conditions: Asthma, cystic fibrosis, diabetes, and heart failure raise your risks for pneumonia.

What Are the Symptoms of Pneumonia?

The general symptoms of bacterial pneumonia can develop quickly and may include:

  • chest pain
  • shaking chills
  • fever
  • dry cough
  • muscle aches
  • nausea/vomiting
  • rapid breathing
  • rapid heartbeat
  • difficulty breathing

Some symptoms may indicate a medical emergency. These symptoms include:

  • skin with bluish tone (from lack of oxygen)
  • blood in sputum (coughed-up mucus)
  • labored breathing
  • high fever (103 °F or higher)
  • confusion
  • rapid heartbeat

How Is Pneumonia Diagnosed?

Pneumonia can be easily overlooked as the cause of an illness because it often resembles a cold or the flu. However, it usually lasts longer and symptoms seem more severe than these other conditions.