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.

Types of pneumonia

There are several different classification schemes: microbiological, radiological, age-related, anatomical, point of acquiring infection. The main classification used in medical journals is that between the point of infection: community-acquired and hospital-acquired. Community-acquired pneumonias are pneumonias in a patient who is not or has not recently been hospitalized, whereas hospital-acquired pneumonias (or nosocomial pneumonias) are found in hospitalized or recently discharged patients. Furthermore, infections in the immunocompromised, as well as aspiration pneumonia, are usually treated as separate disease entities as they have other causal agents, as well as a different clinical course.

Related Topics:
Medical journal - Aspiration pneumonia

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Aside from these, there are several other terms used to classify pneumonias. A lobar pneumonia is an infection that involves, and is limited to, a single lobe of a lung (generally due to Streptococcus pneumoniae). In contrast, multilobar pneumonia involves more than one lobe. Ventilator-associated pneumonia can be considered a subset of hospital-acquired pneumonia; it occurs following intubation and mechanical ventilation for at least 48 hours. "Walking pneumonia" is an outdated term for pneumonia in a patient who is still able to walk—that is, a mild pneumonia, usually due to Mycoplasma. Pneumococcal pneumonia is due to S. pneumoniae (around half of all pneumonias). Finally, atypical pneumonia is due to either Mycoplasma, Chlamydia, or Legionella.

Related Topics:
Lung - Streptococcus pneumoniae - Intubation - Mechanical ventilation - Mycoplasma - Chlamydia - Legionella

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Community-acquired pneumonia

Epidemiology

Community-acquired pneumonia (CAP) is a serious illness. It is the fourth most common cause of death in the UK, and sixth in the USA. 85% of cases of CAP are caused by the typical bacterial pathogens, namely, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. The remaining 15% are caused by atypical pathogens, namely Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella species. Unusual aerobic gram-negative bacilli (for example, Pseudomonas aeruginosa, Acinetobacter, Enterobacter) rarely cause CAP.

Related Topics:
Streptococcus pneumoniae - Haemophilus influenzae - Moraxella catarrhalis - Mycoplasma pneumoniae - Chlamydia pneumoniae - Legionella species - Pseudomonas aeruginosa - Acinetobacter - Enterobacter

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Clinical features

Typical symptoms include cough, purulent sputum production, shortness of breath, pleuritic chest pain, fevers and chills. On examination, one notes rapid respiratory rate and heart rate and signs of pulmonary consolidation. In the elderly, symptoms and signs are sometimes vague and non-specific. They may include headache, malaise, diarrhea, confusion, falling, and decreased appetite. Diagnosis is confirmed by physical examination and chest x-ray. In general, patients who present with symptoms consistent with CAP, without extrapulmonary findings on history, physical examination or in laboratory tests have a CAP caused by a typical pathogen. Patients who have pneumonia plus extrapulmonary physical findings or laboratory features (such as elevations in liver function test results) have an atypical pneumonia.

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Hospital-acquired pneumonia

Hospital-acquired pneumonia, also called nosocomial pneumonia, is a lung infection acquired after hospitalization for another illness or procedure. It is considered a separate clinical entity from CAP because the causes, microbiology, treatment and prognosis are different. Up to 5% of patients admitted to an hospital for other causes subsequently develop a pneumonia. Hospitalized patients have a variety of risk factors for pneumonia, including mechanical ventilation, prolonged malnutrition, underlying cardiac and pulmonary diseases, achlorhydria and immune disorders. Additionally, pathogens thrive in hospitals that could not survive in other environments. These pathogens include resistant aerobic gram-negative rods, such as Pseudomonas, Enterobacter and Serratia, resistant gram positive cocci, such as MRSA. Because of risk factors, underlying morbidity and resistant bacteria, hospital-acquired pneumonia tends to be more deadly than its community counterpart.

Related Topics:
Pseudomonas - Enterobacter - Serratia - MRSA

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Ideal therapy is based on determination of the aetiological agent and its relevant antibiotic sensitivity; however, a specific pathogen is identified in only 50% of patients even with extensive evaluation. Empiric treatment is usually started before laboratory microbiological reports are available as treatment should not be delayed in any patient due to the seriousness of the disease.

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Antibiotics used for hospital-acquired pneumonia include aminoglycosides, fluoroquinolones, carbapenems, and vancomycin. Multiple antibiotics are administered in combination in order to cover all the possible organisms effectively and rapidly, before the infectious agent can be known. Antibiotic choice varies from hospital to hospital as the likely pathogens and resistance patterns vary from place to place.

Related Topics:
Aminoglycoside - Fluoroquinolone - Carbapenem - Vancomycin

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Other pneumonias

• Severe acute respiratory syndrome (SARS)
• Pneumocystis jiroveci pneumonia
• Bronchiolitis obliterans organizing pneumonia
• Eosinophilic pneumonia
• Chemical pneumonia, or more properly chemical pneumonitis, caused by chemical toxins such as pesticides or gasoline which enter the body by inhalation or by skin contact.