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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.

Table of contents
1 Signs and symptoms
2 Diagnosis
3 Classification
4 Types of pneumonia
5 Pathophysiology
6 Therapy
7 Prognosis
8 History of pneumonia
9 References

Signs and symptoms

Symptoms may include: 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.


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).


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

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. 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 resistent aerobic gram-negative rods, such as
Pseudomonas, Enterobacter and Serratia, resistent gram positive cocci, such as ORSA. Because of risk factors, underlying morbidity and resistent bacteria, hospital-acquired pneumonia tends to be more deadly than its community counterpart. 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 resistence patterns vary similarly.

Other pneumonias


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.


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.


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.