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Pneumonia is an infection of the lung tissue and can either affect an entire lobe (lobar pneumonia, thanks to for this image) of the lung or a segment of it (segmental pneumonia). The clinician cannot make this distinction by examination alone, but needs confirmation by lung x-rays, where this distinctions can be readily made.

In the US about 2 million people come down with pneumonia each year and about 50,000 die from it, the 6th most common cause of all deaths (Ref. 9, p. 601). The most common cause of pneumonia in the adult are bacteria, whereas in children and infants viral infections are more common.

Common bacteria causing pneumonia

Streptococcus pneumoniae Chlamydia pneumoniae
Haemophilus influenzae Chlamydia psittaci
Staphylococcus aureus Chlamydia trachomatis
Moraxella catarrhalis Legionella pneumophila
Common viruses causing pneumonia:
respiratory syncytial virus (RSV) parainfluenza virus
influenza A influenza B
Rarer causes of pneumonia:
Mycobacterium tuberculosis Coccidioides immitis
Histoplasma capsulatum Blastomyces dermatitidis
Cryptococcus neoformans Pneumocystis carinii
Aspergillus fumigatus Coxiella burnetii (Q-fever)
SARS coronavirus bird flu (type A, H5N1 strain)


 Pneumonia in a child

Pneumonia in a child

However, there are certain high risk situations where more rare forms of pneumonia occur. For instance in AIDS, where the immune system is weakened from the AIDS virus, interstitial pneumonia with Pneumocystis carinii is very common.

This pathogen, which has been considered to be a protozoan parasite, has recently been shown to have DNA sequences of a fungus type. X-rays show typical interstitial infiltrates (thanks to for this image) on both lungs. Bronchoscopy is indicated to obtain samples from the infected areas for culture and microscopic identification.



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Last modified: September 12, 2014

This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.