What Is Pneumonia? - Definition, Types, Symptoms & Treatment

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

Pneumonia is a serious lung infection that can affect anyone. Read this lesson to learn more about the different types of pneumonia, the symptoms associated with each, and how the infection is treated.

What is Pneumonia?

Pneumonia is a lung infection that can be caused by bacteria, viruses, or fungal infections. The infection may occur in one or both lungs and can be caused by respiratory viruses, the flu virus, as well as a host of others. Once the lungs become infected, they begin filling with fluid, and this is what causes the most severe symptoms of pneumonia. Children, the elderly (people over 65), and people with weakened immune systems are most at risk for developing pneumonia.

Pneumonia is caused by an infection that causes fluids to fill the air sacs in the lungs, as diagrammed here.

Types of Pneumonia

  1. Bacterial: Sometimes bacterial pneumonia begins on its own and sometimes it's caused by another illness, like a cold or the flu. Anyone can catch this type, but the people at the highest risk are those with compromised immune systems. There are many types of bacteria that can cause pneumonia, but the most common form is Streptococcus pneumoniae, at least in adults.
  2. Viral: Viral pneumonia is especially common in children. In most healthy individuals, a viral infection would cause a respiratory infection but not pneumonia. Sometimes viral pneumonia has no early symptoms until the person finds it incredibly difficult to breathe. The flu virus is one virus that can lead to viral pneumonia.
  3. Mycoplasma: This type of pneumonia is caused by mycoplasms, which are neither viruses nor bacteria. Anyone can develop mycoplasma pneumonia, but children and young adults are most susceptible.
  4. Tuberculosis: There is a separate type of pneumonia caused by tuberculosis, and it is a dangerous form unless caught extremely early.
  5. Pneumocystis carinii: This type of pneumonia is caused by a fungus and is often the first visible indicator of the AIDS virus.

Symptoms of Pneumonia

Pneumonia can cause a variety of symptoms, but the most general ones include a cough that produces colored mucus, a fever (higher body temperature than normal), chills, whole-body shaking, and difficulty breathing, especially after physical activity. The fluid in the lungs prevents oxygen from being absorbed by the body, resulting in these overall symptoms. Additional (but less common) symptoms are headaches, sweating, loss of appetite, fatigue, confusion, and chest pains.

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