PCP is a pneumonia caused by the fungal organism Pneumocystis carinii, which is widespread in the environment, and is not a pathogen (does not cause illness) in healthy individuals.

However, in individuals with weakened immune systems due to cancer, HIV/AIDS, solid organ and/or bone marrow transplantation, as well as individuals receiving chronic corticosteroids or other medications that affect the immune system, Pneumocystis carinii may lead to a lung infection.

Individuals with advanced AIDS are of particular interest, since PCP was a relatively rare infection prior to the AIDS epidemic. Before the use of preventive antibiotics for PCP, up to 70% of individuals in the U.S. with advanced AIDS would develop PCP.

PCP in the setting of AIDS usually develops slowly and is less severe -- several weeks of cough, fevers, and progressive shortness of breath, especially with exertion. Individuals with PCP who do not have AIDS usually get sick faster and are more acutely ill.

• fever
• cough -- often mild and dry
• shortness of breath -- especially with exertion (activity)
• rapid breathing

• X-ray of the chest may reveal abnormal lung findings -- yet up to 10% of individuals with PCP in the setting of AIDS may have a normal chest x-ray
• sputum induction: for special stains to detect Pneumocystis carinii
• bronchoscopy (with lavage) -- if sputum induction is negative
• lung biopsy may rarely be needed if the above studies fail to yield a diagnosis
• blood gases which may show decreased oxygen level in blood and helps in determining whether an individual might benefit from corticosteroids

The mainstay of treatment for PCP is antimicrobial therapy. Trimethoprim-sulfamethoxazole is the drug of choice for PCP, and may be given orally or via the intravenous route depending on the severity of the illness.

In individuals with low levels of oxygenation and moderate to severe PCP, corticosteroids are frequently used as well. Other antimicrobials used for the treatment of PCP include: pentamidine, trimethoprim-dapsone, clindamycin, primaquine, and atovaquone.

Pneumocystis carinii pneumonia can be life-threatening, and death may occur due to respiratory failure -- hence early and effective treatment is necessary. For moderate to severe PCP in individuals with AIDS, the use of adjunctive corticosteroids has also led to decreased mortality.

• respiratory failure -- may require mechanical ventilation
• pneumothorax
• pleural effusion (extremely rare)

Individuals with weakened immune systems due to AIDS, cancer, transplantation, or corticosteroid use should notify their physician if they develop cough, fevers, and/or shortness of breath.

While there are many infections that may lead to similar symptoms, a medical evaluation must be performed to rule out opportunistic infections like PCP.

Preventive therapy is recommended for AIDS patients, for individuals on chronic high dose corticosteroids, as well as individuals with previous episodes of PCP.

While the most effective preventive drug is trimethoprim-sulfamethoxazole, other options include dapsone, atovaquone, and pentamidine.