What is Pneumonia?

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Pneumonia is a lung infection that causes inflammation and damage to lung tissue. The lungs are comprised of passages (bronchi) through which air circulates and small sacs (alveoli) where gas exchange occurs.

In a healthy person, the alveoli fill with air during respiration; however in people with pneumonia, the alveoli are already full of pus and fluid which affects gas exchange.

Types of pneumonia

Pneumonia can be classified into two groups depending on the clinical presentation:

  • Community-acquired pneumonia (CAP). Community-acquired pneumonia is characterised by a rapid clinical onset, high fever, pain in one side or transient abdominal pain, rapid breathing (tachypnoea), cough and purulent or brownish phlegm. One example of this common type of presentation is pneumonia induced by Streptococcus pneumoniae (pneumococcus), which is considered the main pneumonia-causing microorganism worldwide.
  • Community-acquired pneumonia with an atypical clinical presentation. This is characterised by a less acute onset, low fever, a barely productive (dry) cough, diarrhoea and/or vomiting. Pneumonias caused by intracellular bacteria, e.g., Mycoplasma pneumoniae or Legionella pneumophila, are known as atypical pneumonias due to their unusual presentation.

How many people are affected by pneumonia?

Pneumonia is a very common infection. According to data from the World Health Organization (WHO), in 2015, pneumonia and influenza were collectively the third highest cause of death worldwide.

The incidence of community-acquired pneumonia (CAP) in Europe is estimated to be 2–10 cases per 1,000 inhabitants/year. Children under 5 years and adults over 65 are the most vulnerable groups.

It is calculated that between 20% and 70% of cases in Spain require hospitalisation and approximately 9% of patients diagnosed with pneumonia have to be admitted to an intensive care unit (ICU) for monitoring.

CAP results in death in 5–7% of cases, but this can increase to 25% for patients admitted to an ICU.   

Substantiated information by:

Antoni Torres Martí
Juan Roselló Sáncho

Published: 20 February 2018
Updated: 20 February 2018


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