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Pneumonia in Immunocompromised People

by Sanjay Sethi, MD

Pneumonia in people whose immune system is weakened or impaired (for example, by AIDS, cancer, organ transplantation, or the use of certain drugs) is often caused by different organisms than those that cause pneumonia in healthy people.

  • Pneumonias due to microorganisms that do not often cause disease in healthy people can occur in people who have a weakened immune system.

  • People have shortness of breath, a dry cough, and often fever.

  • X-rays of the chest are often combined with microscopic examinations of sputum samples to make the diagnosis.

  • Antibiotics or antifungal or antiviral drugs are used to treat this pneumonia, and any immune system problem is treated.

Pneumonia is infection of the lungs. In people with a weakened immune system, pneumonia may be caused by many microorganisms, including those that do not usually cause pneumonia. Many conditions may cause weakness of the immune system, including

  • Cancer and the chemotherapy drugs used to treat cancer

  • Defects in white blood cells

  • Diseases, such as AIDS

  • Certain drugs (such as corticosteroids, chemotherapy drugs, and drugs used to treat autoimmune or connective tissue disorders)


In people with a weakened immune system, pneumonia may be caused by the same microorganisms that cause community-acquired pneumonia but is more often caused by unusual or uncommon organisms.

Pneumocystis jirovecii is a common fungus that may reside harmlessly in the lungs of healthy people. It usually causes pneumonia only when the body’s defenses are weakened because of cancer, use of drugs that alter the immune system, or AIDS. Often, P. jirovecii pneumonia is the first indication that a person with human immunodeficiency virus (HIV) infection has developed AIDS.

Other fungi such as Aspergillus and Candida, bacteria such as Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae, and viruses such as cytomegalovirus and herpes simplex virus also cause pneumonia in people with a weakened immune system.


Most people develop a fever, shortness of breath, and a dry cough. These symptoms can develop rapidly in some cases or slowly, as is often the case with P. jirovecii pneumonia. The lungs may not be able to deliver sufficient oxygen to the blood, leading to shortness of breath that is sometimes severe.


  • Chest x-ray

  • Microscopic examination of a sputum (thick or discolored mucus) sample

The specific problem with the immune system may suggest the organism that is causing the pneumonia.

X-rays show either no abnormality or patchy infection, similar to that which occurs in some viral infections.

The diagnosis is made by microscopic examination of expectorated sputum or from sputum obtained by induction (in which a vapor is used to stimulate coughing) or bronchoscopy (in which an instrument is inserted into the airways to collect a specimen.


  • Antibiotics, antivirals, or antifungals

  • Treatment of any immune system problem

Treatment of pneumonia depends on the

  • Specific immune system problem

  • Severity of illness

  • Organisms that may be causing infection

Doctors usually give an antibiotic that is effective against many organisms (a broad-spectrum antibiotic). If the person's condition does not improve, doctors may add an additional drug that is effective against viruses or fungi.

Even when the pneumonia is treated, the overall death rate is higher than that for people with community-acquired pneumonia because infections are much harder to treat in people with immune system problems and because these people tend to be much more sick, even before onset of pneumonia.

Therapies to improve the immune system are also important for the treatment of pneumonia in people with immune system problems. Drugs that suppress the immune system (such as chemotherapy drugs or drugs used to treat autoimmune disorders) should be temporarily stopped until the infection has resolved.


Doctors often give treatments to help bolster the person's immune system and prevent pneumonia. For example, in people whose immune system has been weakened by cancer treatment, doctors may give a drug, called granulocyte-colony stimulating factor, to enhance the production of white blood cells (the type that fight infection).

People who are at risk of infection should receive vaccinations against pneumococcus and H. influenzae.

The combination antibiotic trimethoprim/sulfamethoxazole can be used to help prevent Pneumocystispneumonia in people at risk. This drug’s side effects, which are particularly common in people who have AIDS, include rashes, a reduced number of infection-fighting white blood cells, and fever. Alternative preventive drug treatments are dapsone, atovaquone, and pentamidine (which can be taken as an aerosol, inhaled directly into the lungs).

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