Pneumonia is an inflammatory illness of the lung. Frequently, it is described as lung parenchyma/alveolar inflammation and abnormal alveolar filling with fluid. The alveoli are microscopic air-filled sacs in the lungs responsible for absorbing oxygen. Pneumonia can result from a variety of causes, including infection with bacteria, viruses, fungi, or parasites, and chemical or physical injury to the lungs. Its cause may also be officially described as idiopathic—that is, unknown—when infectious causes have been excluded.

Typical symptoms associated with pneumonia include cough, chest pain, fever, and difficulty in breathing. Diagnostic tools include x-rays and examination of the sputum. Treatment depends on the cause of pneumonia; bacterial pneumonia is treated with antibiotics.

Pneumonia is a common illness which occurs in all age groups, and is a leading cause of death among the elderly and people who are chronically and terminally ill. Vaccines to prevent certain types of pneumonia are available. The prognosis depends on the type of pneumonia, the appropriate treatment, any complications, and the person's underlying health.

Signs and symptoms

Symptoms of pneumonia need immediate medical evaluation. Physical examination by a health care provider may reveal fever or sometimes low body temperature, an increased respiratory rate, low blood pressure, a high heart rate, or a low oxygen saturation, which is the amount of oxygen in the blood as indicated by either pulse oximetry or blood gas analysis. People who are struggling to breathe, who are confused, or who have cyanosis (blue-tinged skin) require immediate attention.

Physical examination of the lungs may be normal, but often shows decreased expansion of the chest on the affected side, bronchial breathing on auscultation with a stethoscope (harsher sounds from the larger airways transmitted through the inflamed and consolidated lung), and rales heard over the affected area. Percussion may be dulled over the affected lung, but increased rather than decreased vocal resonance (which distinguishes it from a pleural effusion). While these signs are relevant, they are insufficient to diagnose or rule out a pneumonia; moreover, in studies it has been shown that two doctors can arrive at different findings on the same patient.

Diagnosis

If pneumonia is suspected on the basis of a patient's symptoms and findings from physical examination, further investigations are needed to confirm the diagnosis. Information from a chest X-ray and blood tests are helpful, and sputum cultures in some cases. The chest X-ray is typically used for diagnosis in hospitals and some clinics with X-ray facilities. However, in a community setting (general practice), pneumonia is usually diagnosed based on symptoms and physical examination alone. Diagnosing pneumonia can be difficult in some people, especially those who have other illnesses. Occasionally a chest CT scan or other tests may be needed to distinguish pneumonia from other illnesses.