Pneumonia

Pneumonia is an inflammation of the lungs. The term is almost always used to refer specifically to infections of the lungs caused by bacteria, viruses, fungi or other parasites; however, it can also refer to lung injury caused by physical or chemical irritants, in which case the term pneumonitis is used to differentiate the condition from infectious pneumonia. This article uses pneumonia only in the first sense, that of infection. Pneumonia may occur in people of all ages, although young children, the elderly, and immunocompromised patients are especially at risk. Antimicrobial drugs are often used to treat pneumonia.

Aetiology

There are over one hundred organisms known to cause pneumonia. However, relatively few are responsible for the majority of cases, and classifying the pneuomonias as mentioned above helps to shorten the list of likely offenders. Of these myriad pathogens, the most common cause of community-acquired pneumonia (the most common form of pneumonia overall) is Streptococcus pneumoniae. The major classes of microorganisms causing pneumonia are Gram-positive bacteria, Gram-negative bacteria, the so-called "atypical" bacteria, viruses, and opportunistic pathogens. This classification is important because different antimicrobial drugs are effective against different classes.

Related Topics:
Streptococcus pneumoniae - Gram-positive bacteria - Gram-negative bacteria - Virus

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The major Gram-positive bacteria are Streptococcus pneumoniae, Staphylococcus aureus (often seen in more serious pneumonias, and Streptococcus pyogenes. Gram-negative bacteria are seen less frequently; more common pathogens include Haemophilus influenzae, Klebsiella pneumoniae, Pseudomonas aeruginosa, Moraxella catarrhalis, and Neisseria meningitidis. Escherichia coli, Proteus, and Enterobacter are responsible for a smaller portion of pneumonias. The atypical agents are Chlamydophila pneumoniae, Mycoplasma pneumoniae, and Legionella pneumophila.

Related Topics:
Streptococcus pneumoniae - Staphylococcus aureus - Streptococcus pyogenes - Haemophilus influenzae - Klebsiella pneumoniae - Pseudomonas aeruginosa - Moraxella catarrhalis - Neisseria meningitidis - Escherichia coli - Chlamydophila pneumoniae - Mycoplasma pneumoniae - Legionella pneumophila

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Viral pneumonia is usually caused by influenza virus, respiratory syncytial virus (RSV), adenoviruses, and varicella-zoster virus (direct VZV pneumonia is rare, but well recognosied is a staphylococcal secondary infection in cases of chicken pox. Herpes simplex virus is a rare cause of pneumonia. The above agents all cause pneumonia in people with intact immune systems. In those whose immune system is impaired (for instance, due to infection with HIV or as a result of taking immunosuppresive drugs), opportunistic pathogens can cause pneumonia. Major ones include the Pneumocystis jiroveci (a fungus), Mycobacterium avium (a bacterium), and cytomegalovirus (CMV, a virus).

Related Topics:
Influenza virus - Respiratory syncytial virus - Adenovirus - Varicella-zoster virus - Secondary infection - Chicken pox - Herpes simplex virus - Immune system - HIV - Immunosuppresive drug - Pneumocystis jiroveci - Fungus - Mycobacterium avium - Cytomegalovirus

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