What is pneumonia and what causes it?
Pneumonia is a lower respiratory tract infection that mainly affects the lungs. The lungs are made up of small sacs called alveoli, which are filled with air when a healthy person breathes in. When an individual has pneumonia, the alveoli are filled with pus and fluid, which makes breathing painful and limits the amount of oxygen they can take into the body. Pneumonia is caused by a number of infectious agents, mainly by certain bacteria and viruses (box below). In children or adults whose immunity is weak, other organisms such as fungi can cause a rare form of pneumonia, which may be responsible for at least one quarter of all pneumonia deaths in HIV-infected infants.
Major bacterial or viral causes of pneumonia
Bacterial causes (the major causes of death from pneumonia)
- Streptococcus pneumoniae – the most common cause of bacterial pneumonia.
- Haemophilus influenzae type b (Hib) – the second most common cause of bacterial pneumonia.
- Respiratory syncytial virus – the most common viral cause of pneumonia.
Pneumonia is the number one cause of death among children worldwide: globally, it causes an estimated 1.6 million child deaths every year. It is also among the top causes of illness and death in adults.
Viral infections often come on gradually and may worsen over time. The common symptoms include cough, fever, chills, headaches, loss of appetite and wheezing.
Which of the bacterial causes of pneumonia can be prevented by immunization?
Vaccines exist to protect children from bacterial pneumonia caused by Haemophilus influenzae type b (Hib) or Streptococcus pneumoniae.
Immunization against measles also helps to protect children from complications, which include pneumonia and AOM.