Introduction
Pneumonia is a common lower respiratory tract infection, characterised by inflammation of the lung tissue. It is almost always an acute infection, and almost always caused by
bacteria. Diagnosis is typically confirmed via
chest x-ray.
- Pneumonia is the most fatal hospital acquired infection
- As well as bacteria, other causes include viruses, fungus and parasites.
Epidemiology
- Pneumonia is a dangerous condition, and is responsible for many deaths of patients over the age of 80
- Deaths amongst younger populations have dramatically decreased with the advent of antibiotics.
- Incidence is 1-3 per 1000 (i.e.. 0.1-03% of people have pneumonia at any one time)
- The incidence of bacterial pneumonia amongst those with HIV is higher than in the general population, particularly in IV drug users with HIV. However, the causatory organisms are the same.
- Most cases caused by bacteria, about 15% are viral
Classification
This can be done either by anatomical location – e.g. if one particular lobe is affected, then it is localised pneumonia, or it can be a more diffuse pneumonia, affecting the lobules and bronchioles; in which case it is called bronchopneumonia.
You can also classify them according to their aetiology; e.g. pneumococcal or atypical (e.g. caused by
Chlamydia, legionella, coxiella burnetti). Atypical are so called because they are caused by atypical organisms, but the infection itself will tend to have similar symptoms. Many people have now dropped the use of the word ‘atypical’.
75% of cases are pneumococcal in cause, and 20% atypical. The remaining 5% may be caused by aspiration of vomit, radiotherapy and
allergic mechanisms.
However, the most useful distinction is between community acquired and hospital acquired pneumonias. The difference between the two is in the causatory organism.
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Community Acquired
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Hospital Acquired
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General Info
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Defined as pneumonia that develops 48h after admission
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Prognosis
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Generally good, especially for younger patients. S pneumoniae and viral pneumonias are still fatal in older patients.
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Generally poor, due to co-morbidities (due to nature of hospital acquired infections), older age range of patients, and resistance of organisms
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Common organisms
Note that in many cases (particularly in community acquired), the exact organism is not identified
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Streptococcus pneumoniae, haemophilus influenzae
Anaerobes are rare
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Drug resistant organisms are more common, and more dangerous
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Rare organisms
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Chlamydia pneumoniae (common in institutions – e.g. collegues, military camps – mild), mycoplasma pneumoniae, legionella
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As above
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Precipitating factors
- Strep pneumoniae infection often follows viral infection with influenza or parainfluenza.
- Hospitalisation! – hospital acquired infection is often with Gram-negative organisms
- Cigarette smoking - this is the most important risk factor for pneumococcal disease
- Alcohol excess
- Bronchiectesis (e.g. in CF)
- Bronchial obstruction (e.g. carcinoma)
- Immunosupression
- IV drug use
- Dysphagia (both oesophageal and co-ordination disorders – leading to aspiration)
Symptoms
- Typically the same for hospital acquired / non-hopsital acquired cases
- Shortness of breath
- Cough
- May be productive in adolescents and adults - Purulent sputum possible
- Often dry in infants and the elderly
- Fever
- Rigors
- Vomiting
- Headache
- Loss of appetite
- Very occasionally – haemoptysis
- Pleuritic chest pain – which may on occasion radiate to the shoulder (if diaphragm is involved) or the anterior abdominal wall
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