Pneumonia is an inflammatory condition of the lung. It is often characterized as including inflammation of the parenchyma of the lung (that is, the alveoli) and abnormal alveolar filling with fluid (consolidation and exudation).

The alveoli are microscopic air filled sacs in the lungs responsible for gas exchange. 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 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.

Streptococcus pneumoniae and Haemophilus influenzae type b (Hib) are the leading bacterial pathogens. Other bacteria (Staphylococcus aureus, and gram-negative pathogens) more often affect newborns and malnourished children. Respiratory viruses (RSV, influenza, parainfluenza, and adenovirus) can be identified in approximately a quarter of children with pneumonia but are much less likely to cause fatal infection than are the bacterial pathogens.

Each year, there are more than 150 million episodes of pneumonia in young children in developing countries, and more than 11 million children need hospitalization for pneumonia.

Each year, acute respiratory infections cause approximately 2 million deaths among children <5 years old and are the leading cause of death in this age group. About 1% of pneumonia cases result in sequelae or after-effects of the condition (e.g., damaged airways), which increases the risk of recurrent infections.

Infants (especially premature or low birth weight). Nearly 75% of pneumonia deaths occur among infants under 1 year old. Risk also increases with malnutrition, malaria, and suppressed immunity. The burden of pneumonia among children with HIV infection is high.

Page last edited: 03 May 2011