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Pneumocystis Carinii Pneumonia (PCP)


Pneumocystis Carinii Pneumonia (PCP) is pneumonia in premature infants and immunocompromised children and adults caused by a fungus.


Pneumocystis carinii is a common microorganism that exists in rats, guinea pigs, monkeys, dogs, sheep, humans, and other animals. Most people are infected with Pneumocystis carinii during childhood and develop no symptoms. In North America, 65 to 100 percent of children have been infected with Pneumocystis carinii by the age of four. In people with adequately functioning immune systems, Pneumocystis carinii remains a harmless, latent, lifelong infection. It generally causes disease only in people with impaired immune systems.

Active PCP was first observed in infants after World War II who were immune-suppressed due to malnutrition. It has also been seen occasionally in patients whose immune systems have been suppressed by diseases such as leukemia, Hodgkin's disease, other cancers, or in patients using immune-suppressant drugs as part of organ transplantation. People who are immune-suppressed due to HIV infection have been particularly vulnerable to PCP.

In rare cases, Pneumocystis carinii has been reported in parts of the body other than the lungs - this is called extrapulmonary pneumocystosis.


In the immune-suppressed person, Pneumocystis carinii causes disease by growing and filling the alveoli of the lungs. Alveoli are small sacs in the lung that are lined with blood vessels. Oxygen inhaled in the lungs diffuses across the walls of the alveoli into the tiny blood vessels that line each sac. Carbon dioxide is expelled from the blood by a similar mechanism.

If a large proportion of alveoli are filled with microorganisms and the fluid by-products of inflammation, the blood can neither get enough oxygen nor get rid of excess carbon dioxide.

The specific mode of transmission in primary infection is unknown but the evidence suggests airborne transmission. After asymptomatic primary infection, presumably inactive organisms are sparsely distributed in the alveoli.

It is unclear whether acute infection in older children and adults results from new infection or from reactivation of latent infection.


Pneumocystis carinii pneumonia usually begins with mild but gradually worsening symptoms. These include:

  • Dyspnea (shortness of breath) is the most common symptom. This is noticed initially during exertion but as the disease progresses it occurs even at rest
  • Cough associated with PCP usually produces no mucus or, in patients who smoke, only thin, clear mucus
  • Tachypnea (very rapid breathing)
  • Fevers
  • Chills
  • Sweats
  • Progressive, profound fatigue
  • Cyanosis (bluish discoloration from lack of oxygen) around mouth, extremities (hands or feet), and mucous membranes

Respiratory symptoms are not always the first or most prominent sign of PCP. Many people have a few weeks or months of fever, fatigue and weight loss (constitutional symptoms) before respiratory symptoms develop.


Tests used to diagnose PCP include chest X-rays, pulmonary function tests, induced sputum tests, and bronchoscopy.


The first choice for treatment is usually trimethropim/sulfamethoxazole (Bactrim, Septra) given for 14 to 21 days. Pentamidine isethionate is an equally effective medication and is also given for 14 to 21 days. Severe adverse reactions can occur in up to 50 percent of patients receiving either medication.

Atovaquone is used for patients who cannot tolerate Bactrim/Septra or pentamidine.

Some patients with severe PCP may receive a corticosteroid (prednisone). Hospitalization may be required and supplemental oxygen may be necessary.


Are there signs and symptoms of PCP?

Do you recommend further diagnostic tests?

Should preventive measures be taken?

What drugs are available?

What are the side effects of these drugs?

Primary PCP prophylaxis is offered for immunocompromised patients. It is generally offered to HIV patients with CD4 counts below 200 cells/microliter, or less than 14 percent CD4 lymphocyte counts, or weight loss or oral candidiasis. Medications include Bactrim/Septra, dapsone, or aerosolized pentamidine.

Patients with a history of PCP should receive secondary prophylaxis for that disease.