Pneumonia is a lung infection that can be caused by many different germs, including bacteria, viruses, and fungi.

This article discusses describes pneumonia that occurs in a person whose ability to fight infection is greatly reduced because their immune system is weakened and not working properly. Such disease is referred to as "pneumonia in an immunocompromised host."

See also:

• Hospital-acquired pneumonia
• Pneumocystis carinii pneumonia
• Pneumonia - cytomegalovirus
• Pneumonia
• Viral pneumonia
• Walking pneumonia

A person whose immune system is not working well is less able to fight off germs. Because of this, they are more likely to become infected by germs that typically do not cause disease in healthy people. They are also more vulnerable to the usual causes of pneumonia, which can affect anyone.

Your immune system may be weakened or not work well because of:

• Bone marrow transplant
• Certain medications (including steroids and those used to treat cancer)
• Chemotherapy
• HIV infection
• Leukemia, lymphoma, and other conditions that harm your bone marrow
• Organ transplant (such as kidney, heart, or lung)