Pneumonia – colloquially known as pneumonia – (synonyms: Bronchopneumonia; Lobar pneumonia; ICD-10 J18.-: Pneumonia, causative agent unspecified; J12.-: Viral pneumonia, not elsewhere classified; J16.-: Pneumonia due to other infectious agents, not elsewhere classified; J17.-: Pneumonia due to diseases classified elsewhere) is an inflammation of the lung tissue (ancient Greek πνεύμων pneumōn, German “lung”), usually caused by infection with bacteria, viruses, or fungi, and less commonly by allergies and chemical or physical irritants. Based on their etiology, pneumonias are commonly divided into three categories:
- Community-acquired pneumonia (AEP; CAP).
- Hospital-acquired nosocomial pneumonia (“hospital acquired pneumonia”, HAP), which is one of the most common infections occurring during a hospital stay.
- Pneumonia in the immunocompromised (including neutropenic patients after chemotherapy, after transplantation, and patients with chronic immunosuppressive therapy for systemic diseases).
Approximately 70% of pneumonias are caused by bacteria. In about 25-45% of cases, pneumococci are the causative agents of community-acquired pneumonia, 5-20% are caused by Haemophilus influenzae and 5-25% by viruses (mainly influenza viruses). The following forms of pneumonia are distinguished:
- Acute or chronic form
- Primary pneumonia – occurs without the presence of an underlying disease.
- Secondary pneumonia – occurs in patients with existing pre-existing conditions.
- Alveolar pneumonia (“pneumonia affecting the alveoli”).
- Lobar pneumonia – form of progression in which the inflammation of the lung tissue affects entire lobes of the lung.
- Bronchopneumonia – form of progression in which the inflammation affects the surroundings of bronchi in a focal form.
- Interstitial pneumonia – pneumonia, which does not affect the alveoli (alveoli), but the interstitium (connective tissue layer between the alveoli and blood vessels).
Furthermore, there are the so-called atypical pneumonias. Atypical pneumonias are mainly caused by atypical pathogens such as Mycoplasma (5-15% of cases), Legionella, Chlamydia or Rickettsia. One fifth of all pneumonias are atypical pneumonias. A special form of pneumonia is nosocomial pneumonia (hospital-acquired pneumonia, HAP), which is one of the most common infections occurring during hospitalization. Seasonal peak of the disease: Pneumonia occurs more frequently during the cold season. Frequency peak: The disease occurs predominantly in infants, small children and the elderly. In Germany, approximately 400,000 to 600,000 people contract pneumonia each year. The incidence (frequency of new cases) for community-acquired pneumonia (CAP) is 8-10 cases per 1,000 inhabitants per year (in Germany). The incidence for nosocomial pneumonia is 5.4 per 1,000 ventilator days in invasively ventilated patients. Course and prognosis: Pneumonia is the number one cause of death among infectious diseases in industrialized countries. This is because critically ill and bedridden patients in particular frequently develop pneumonia nosocomially (acquired in hospital) as a complication. Very resistant pathogens are often the triggers. In otherwise healthy people, pneumonia usually heals without consequences. The mortality rate for primary community-acquired pneumonia (AEP) is less than 0.5%. When hospitalized, the lethality of patients with CAP is 10-20%.The prognosis for secondary and nosocomial pneumonia is rather poor. The CRB-65 and CURB-65 prognosis scores have proven useful in assessing prognosis (see “Physical examination“). Vaccination: Vaccination against the most common triggers, pneumococci, is available. Especially young children up to 2 years of age, persons older than 60 years and people with congenital or acquired immune deficiency (e.g. in case of HIV disease) as well as cardiovascular diseases should be vaccinated.
