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Pneumonia is defined as an infection involving the alveoli of the lungs. It occurs in patients of all age groups, but young children and the elderly, as well as immunocompromised and immune deficient patients, are especially at risk. Causal therapy is with antibiotics.

Signs and symptoms

Symptoms may include:

• Common
  • Cough with greenish or yellow mucus
  • Fever with shaking chills (rigors)
  • Sharp or stabbing chest pain, worsened by deep breaths or coughs
  • Rapid, shallow breathing
  • Shortness of breath
• Rarer
  • Bloody mucus
  • ]
  • Excessive sweating and clammy skin
  • Loss of appetite
  • Excessive fatigue

Pneumonia can progress to sepsis ("blood poisoning") and acute respiratory distress syndrome if untreated. These are the main causes of death in patients with untreated pneumonia.

Diagnosis

For the diagnosis of pneumonia, an infiltrate on an X-ray of the chest is the gold standard. Supportive diagnostic tests are microbiological culture of sputum and/or blood. Blood tests are generally performed when a pneumonia is suspected: a full blood count often showns neutrophilia (except in some immunocompromised and all neutropenic patients). Renal function may have deteriorated if there is sepsis. Electrolytes can show hyponatremia (low sodium levels); this is often due to secretion of antidiuretic hormone by pulmonary tissue.

In nosocomial (hospital-acquired) pneumonia and the pneumonias of the immunocompromised, diagnosis can be difficult, and CT scanning of the lungs can be required to differentiate possible causes (e.g. pulmonary embolism). CT scanning is also used when the symptoms and physical examination point at possible different causes for the complaints (e.g. vasculitis, sarcoidosis, lung cancer).

Classification

There are several different classification schemes: microbiological, radiological, age-related, anatomical, point of acquiring infection. Generally, the following types are used:

• lobar - pneumonia that results in the consolidation of a pulmonary lobe (generally due to Streptococcus pneumoniae)
• multilobar - pneumonia that results in the consolidation of more than one lobe
• community-acquired - pneumonia in a patient who is not or has not recently been in the hospital
• hospital-acquired or nosocomial - pneumonia in a patient in a hospital (or recently discharged)
• "walking" - outdated term, pneumonia in a patient who is still able to walk, a mild pneumonia, usually due to mycoplasma
• pneumococcal - pneumonia due to S. pneumoniae.
• atypical - pneumonia due to either Mycoplasma, Chlamydia or Legionella.

The main classification used in medical journals is that between the point of infection: community-acquired and hospital-acquired.

Types of pneumonia

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.
• 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 vague and non-specific. They may consist of headache, malaise, diarrhea, confusion, falling, and decreased appetite. Diagnosis is confirmed by chest x-ray.

Hospital-acquired pneumonia

To be added

Other pneumonias

On February 27th 2003, severe acute respiratory syndrome (SARS), a new form of atypical pneumonia, was first documented by Dr. Carlo Urbani. This worried doctors who feared that it may become a pandemic, but by July it appeared to be contained. The most common cause of community-acquired pneumonia is Streptococcus pneumoniae, also known as Pneumococcus.

AIDS patients frequently contract pneumocystis pneumonia, an otherwise rare form of the disease.

Pathophysiology

Pneumonia is an infectious disease by definition, and whether a patient is prone to develop pneumonia depends on the presence of pathogens but equally on the patient's immune system and other factors. Most pneumonias are not epidemic, although infection with influenza virus can be defined as such.

Breathing problems, as often present in patients after a stroke, in Parkinson's disease, hospitalisation or surgery and mechanical ventilation can all increase the likelihood of pneumonia. Similarly, inability to clear sputum (as in cystic fibrosis) or retention of sputum (as in bronchiectasis) can lead to pneumonia.

After splenectomy (removal of the spleen), a patient is more prone to pneumonia due to the spleen's role in developing immunity against the polysaccharides on pneumococcus bacteria.

Therapy

Antibiotics are the only causal therapy for pneumonia. The exact type of antibiotics that are used depend on the nature of the pneumonia and the immune status of the patient. Amoxicillin is used as first-line therapy in the vast majority of community patients, sometimes with added clarithromycin. In hospitalised patients and immune deficient patients, local guidelines generally determine which combination of (generally intravenous) antibiotics is used.

Prognosis

The clinical state of the patient at time of presentation is a strong predictor of the clinical course. Many clinicians use the Pneumonia Severity Score to calculate whether a patient requires admission to hospital, based on the severity of symptoms, underlying disease and age (Halm et al).

History of pneumonia

Before the advent of antibiotics, pneumonia was often fatal. When penicillin was discovered in the 20th century, it was the first causal therapy. Most community-acquired strains of S. pneumoniae are still penicillin-sensitive.

References

• Halm EA, Teirstein AS. Management of community-acquired pneumonia. N Engl J Med 2002;347:2039-45.

• Pulmonology