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Pneumonia is an infection of the lungs that can be caused by many different micro-organisms, including viruses, bacteria, parasites and fungi.

What is going on in the body? 
Pneumonia is a fairly common infection that affects people of all ages. Some of its more common causes are:
  • viruses, such as respiratory syncytial virus, parainfluenza viruses, influenza A and adenovirus
  • bacteria, such as Streptococcus pneumoniae, Staphylococcus aureus and Haemophilus influenzae
  • organisms similar to bacteria, such as Mycoplasma pneumoniae, Chlamydia and Mycobacteria
  • parasites, such as Pneumocystis carinii
  • fungi
Usually these organisms are spread by contact with people who are infected by them. Some can be picked up from the environment, though. Others are found in every body, but only cause disease in certain situations. One example of this is aspiration pneumonia. It occurs when a person inhales secretions carrying bacteria, usually from the mouth. Generally, this happens when a person is not completely conscious after a stroke or seizure (convulsions) or due to drug or alcohol intoxication. The inhaled bacteria cause infection.

Pneumonia can sometimes lead to complications, such as effusion (fluid in the lungs) or empyema, which are pockets of fluid or pus around the lung, or an abscess, an infected area in the lung.

What are the signs and symptoms of the infection? 
  • fever
  • shortness of breath
  • cough
  • chest pain
  • vomiting

What are the causes and risks of the infection? 
Many organisms can cause pneumonia. Some conditions or activities make it more likely that a person will get pneumonia more often or more severely, including:
  • a weakened immune system
  • smoking
  • old age
  • abnormal anatomy in the lungs
  • alcohol abuse
What can be done to prevent the infection? 
The influenza, or flu, vaccine and the pneumococcal vaccine effectively prevent pneumonia caused by influenza A and Streptococcus pneumoniae.

How is the infection diagnosed? 
Usually pneumonia is diagnosed by physical examination and a history of symptoms. A chest X-ray can help confirm the diagnosis. Often a specific organism is not identified. Sometimes an organism can be found through blood tests or cultured (grown in the laboratory) from mucous that is coughed up or from blood.

What are the long-term effects of the infection? 
Usually, there are no long-term effects. Sometimes, though, an empyema or abscess can leave a person with decreased lung function.

What are the risks to others? 
Some of the organisms that cause pneumonia can be spread from person to person through coughs or sneezes that send infected droplets into the air.

What are the treatments for the infection? 
  • There are medications designed to combat many of the organisms that cause pneumonia, except viruses.
  • Empyemas may need to be drained with a needle or a tube placed in the chest.
  • Sometimes abscesses must be surgically removed.
What are the side effects of the treatments? 
Specific side effects depend on the medication chosen.

Author: Danielle Zerr, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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