Abstract
Pneumonia occurs frequently in immunocompromised patients and often shows a complicated course of disease when compared to immunocompetent persons. The type of pathogen involved is directly associated with the type of immunosuppression and includes a wide variety of pathogens. Congenital and primary immunodeficiencies often appear during childhood. Acquired immunodeficiencies are most commonly caused by immunosuppressive medication. The concept of immunosuppression can be extended to patients with COPD or elderly patients because the variety of pathogens and specific features regarding frequency and course of the disease are similar to immunosuppressed patients. Computed tomography can provide an indication of the pathogen and is superior to the chest x‑ray in this respect. Blood cultures, antigen and PCR tests are non-invasive diagnostic tools for pathogen diagnostics. Invasive tests include fiberoptic bronchoscopy and complete the diagnostic methods of identifying the causative pathogen.