What are the Three Major Causes of Pneumonia?

Reviewed on 1/6/2021

What is pneumonia?

Pneumonia is an infection that affects one or both lungs causing them to fill with pus or liquid. The three main causes of pneumonia are bacteria, viruses, or fungi. Treatment is depends on the cause.
Pneumonia is an infection that affects one or both lungs causing them to fill with pus or liquid. The three main causes of pneumonia are bacteria, viruses, or fungi. Treatment depends on the cause.

Pneumonia is a type of infection that affects your lungs. It can affect one or both lungs. It causes the air sacs in the lungs, called alveoli, to fill with pus or other liquid. 

Pneumonia is caused by bacteria, viruses, fungi, or, more rarely, parasites. People of all ages can develop pneumonia. In some cases, it is mild and not much worse than a bad cold. In others, it can be life-threatening. 

Older people and young children are most at risk of developing severe pneumonia. It can also be very serious for people with underlying chronic health problems or a weakened immune system.

Signs and symptoms of pneumonia

The symptoms of pneumonia may include any combination of the following:

Types of pneumonia

One way doctors classify pneumonia is based on where or how you got it. Knowing this can help your doctor decide on a course of treatment for your pneumonia. 

Community-acquired pneumonia

This type of pneumonia occurs in a community setting, which is defined as somewhere other than a hospital, rehabilitation center, nursing home, or other types of healthcare facilities. 

Hospital-acquired pneumonia

This type of pneumonia happens when you catch it while you're in a hospital or another type of healthcare facility, such as a nursing home. Hospital-acquired pneumonia develops in people at least 48 hours after being admitted. It does not include people who develop pneumonia while they are on a ventilator, as that is a separate type of pneumonia. 

Ventilator-associated pneumonia

This occurs when people who are on a ventilator develop pneumonia. It occurs at least 48 hours after intubation, which is when the ventilator tube is placed in the airway so that a ventilator can assist with breathing. 

Aspiration pneumonia

Aspiration pneumonia happens when food, liquid, or vomit is inhaled into the lungs. When this happens, a healthy respiratory system can usually clear it up on its own, but in some cases, an infection develops

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Causes of pneumonia

Regardless of where it's acquired, pneumonia has three primary causes and a fourth, much rarer, cause: 

Bacterial pneumonia

  • Most commonly caused by Streptococcus pneumoniae 
  • Can also be caused by Mycoplasma pneumoniae, a bacterium that causes a milder form of pneumonia
  • Can also be caused by Chlamydophila pneumoniae, which also causes milder pneumonia
  • More rarely caused by Legionella pneumophila, also known as Legionnaires’ Disease, caused by exposure to contaminated water 

Viral pneumonia

Fungal pneumonia

  • Most common in people with chronic health problems or weakened immune systems, such as occurs with HIV/AIDS
  • Also occurs in people who are exposed to large amounts of fungi in contaminated soil or bird droppings

Parasitic pneumonia 

  • Rare cause of pneumonia, almost always occurs in people with compromised immune systems
  • Parasites get into the body through the skin or by being swallowed and travel to the lungs

When to see a doctor for pneumonia

You should call your doctor if you have a cough that doesn't improve, shortness of breath or difficulty breathing, chest pain, fever, or you feel worse after having a cold.

Diagnosing pneumonia

Your doctor may be able to diagnose pneumonia by listening to your symptoms and doing a physical exam. Other tests may be done, including a chest X-ray, blood tests, sputum culture, which is testing the mucus you cough up, and pulse oximetry, which tests the oxygen level in your blood.

Treatments for pneumonia

Treatment for pneumonia depends on the cause. 

Bacterial pneumonia

Bacterial pneumonia is generally treated with antibiotics. 

Viral pneumonia

Antibiotics are not effective against viral pneumonia, so they usually get better on their own. Sometimes doctors prescribe antivirals for viral pneumonia. 

Fungal pneumonia

Fungal pneumonia is treated with an antifungal medication that is appropriate for the type of fungus causing pneumonia. 

Parasitic pneumonia 

Treatment for parasitic pneumonia will depend on the type of parasite involved and the underlying issues that weakened the immune system. 

Symptomatic relief

Regardless of the cause or treatment of pneumonia, most people can find symptomatic relief with the following measures:

  • Drink plenty of liquids, including hot liquids such as tea.
  • Take acetaminophen or ibuprofen to control fever.
  • Inhale the steam from a hot shower or use a humidifier
  • Get lots of rest.
  • Don't take cough medicine without talking to your doctor. Coughing helps your body fight the infection. 
  • Take honey for a cough or sore throat, but don't give honey to children under the age of one.

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References
American Family Physician: "Community-Acquired Pneumonia in Adults: Diagnosis and Management."

American Lung Association: "Pneumonia."

Biomed Research International: "Parasitic Pneumonia and Lung Involvement."

Centers for Disease Control and Prevention: "Causes of Pneumonia."

Craig Hospital: "Hospital Acquired Pneumonia (HAP) Prevention."

John Hopkins Medicine: "Pneumonia."

National Heart, Lung, and Blood Institute: "Pneumonia."

Northwestern Medicine: "What is Aspiration Pneumonia?"

Pediatrics in Review: "Pneumonia."

StatPearls: "Bacterial Pneumonia."

StatPearls: "Pediatric Pneumonia."

StatPearls: "Viral Pneumonia."

World Health Organization: "Pneumonia."

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